WO2019052973A1 - Dibenzofuran and dibenzothiophene derivatives - Google Patents

Abstract

The present invention relates to dibenzofuran and dibenzothiophene derivatives of the general formula (I) in which the occurring groups and parameters have the meanings indicated in claim 1, to the use thereof in liquid-crystalline or mesogenic media, to liquid-crystal- line or mesogenic media comprising these derivatives, and to electro-optical display elements containing these liquid-crystalline or mesogenic media.

Description

Dibenzofuran and Dibenzothiophene Derivatives

The present invention relates to dibenzofuran and dibenzothiophene derivatives, to the use thereof in liquid-crystalline or mesogenic media, to liquid-crystalline or mesogenic media comprising these derivatives, and to electro-optical display elements containing these liquid-crystalline or mesogenic media.

Liquid crystals have found widespread use since the first commercially usable liquid-crystalline compounds were found about 30 years ago.

Known areas of application are, in particular, displays for watches and pocket calculators, and large display panels as used in railway stations, airports and sports arenas. Further areas of application are displays of portable computers and navigation systems and video applications. For the last-mentioned applications in particular, high demands are made of the response times and contrast of the images.

The spatial arrangement of the molecules in a liquid crystal has the effect that many of its properties are direction-dependent. Of particular importance for use in liquid-crystal displays are the optical, dielectric and elasto- mechanical anisotropies. Depending on whether the molecules are oriented with their longitudinal axes perpendicular or parallel to the two plates of a capacitor, the latter has a different capacitance; in other words, the dielectric constant ε of the liquid-crystalline medium has different values for the two orientations. Substances whose dielectric constant is larger when the longitudinal axes of the molecules are oriented perpen- dicular to the capacitor plates than when they are oriented parallel are known as being dielectrically positive. Most liquid crystals used in conventional displays fall into this group. Both the polarisability of the molecule and the permanent dipole moment play a role for the dielectric anisotropy. On application of a voltage to the display, the longitudinal axis of the molecules orients itself in such a way that the larger of the dielectric constants becomes effective. The strength of the interaction with the electric field depends on the difference between the two constants. In the case of small differences, higher switching voltages are necessary than in the case of large differences. The introduction of suitable polar groups, such as, for example, nitrile groups or fluorine, into the liquid-crystal molecules enables a broad range of working voltages to be achieved.

In the case of the liquid-crystalline molecules used in conventional liquid- crystal displays, the dipole moment oriented along the longitudinal axis of the molecules is larger than the dipole moment oriented perpendicular to the longitudinal axis of the molecules. The orientation of the larger dipole moment along the longitudinal axis of the molecule also determines the orientation of the molecule in a liquid-crystal display in the field-free state. In the most widespread TN ("twisted nematic") cells, a liquid-crystalline layer with a thickness of only from about 5 to 10 m is arranged between two flat glass plates, onto each of which an electrically conductive, transparent layer of tin oxide or indium tin oxide has been vapour-deposited as electrode. A likewise transparent alignment layer, usually consisting of a plastic (for example polyimides), is located between these films and the liquid-crystalline layer. This alignment layer serves to bring the longitudinal axes of the adjacent crystalline molecules into a preferential direction through surface forces in such a way that, in the voltage-free state, they lie uniformly on the inside of the display surface with the same alignment in a flat manner or with the same small tilt angle. Two polarisation films which only enable linear-polarised light to enter and escape are adhesively bonded to the outside of the display in a certain arrangement. By means of liquid crystals in which the larger dipole moment is oriented parallel to the longitudinal axis of the molecule, very high-performance displays have already been developed. In most cases here, mixtures of from 5 to 20 components are used in order to achieve a sufficiently broad temperature range of the mesophase and short response times and low threshold voltages. However, difficulties are still caused by the strong viewing-angle dependence in liquid-crystal displays as are used, for example, for laptops. The best imaging quality can be achieved if the surface of the display is perpendicular to the viewing direction of the observer. If the display is tilted relative to the observation direction, the imaging quality drops drastically under certain circumstances. For greater comfort, attempts are being made to make the angle through which the display can be tilted from the viewing direction of an observer as large as possible. Attempts have recently been made to improve the viewing-angle

dependence using liquid-crystalline compounds whose dipole moment perpendicular to the longitudinal axis of the molecules is larger than that parallel to the longitudinal axis of the molecule. In the field-free state, these molecules are oriented perpendicular to the glass surface of the display. In this way, it has been possible to achieve an improvement in the viewing- angle dependence. Displays of this type are known as VA-TFT ("vertically aligned") displays. Also known are so-called IPS ("in-plane switching") displays, which contain an LC layer between two substrates with planar orientation, where the two electrodes are arranged on only one of the two substrates and preferably have interdigitated, comb-shaped structures. On application of a voltage to the electrodes an electric field with a significant component parallel to the LC layer is generated between them. This causes realignment of the LC molecules in the layer plane. Furthermore, so-called FFS ("fringe-field switching") displays have been reported (see, inter alia, S.H. Jung et al., Jpn. J. Appl. Phys., Volume 43, No. 3, 2004, 1028), which contain two electrodes on the same substrate, one of which is structured in a comb- shaped manner and the other is unstructured. A strong, so-called "fringe field" is thereby generated, i.e. a strong electric field close to the edge of the electrodes, and, throughout the cell, an electric field which has both a strong vertical component and also a strong horizontal component. FFS displays have a low viewing-angle dependence of the contrast. FFS displays usually contain an LC medium with positive dielectric anisotropy, and an alignment layer, usually of polyimide, which provides planar alignment to the molecules of the LC medium.

Another type of FFS displays has been disclosed that has a similar electrode design and layer thickness as FFS displays, but comprises a layer of an LC medium with negative dielectric anisotropy instead of an LC medium with positive dielectric anisotropy (see S.H. Lee et al., Appl. Phys. Lett. 73(20), 1998, 2882-2883 and S.H. Lee et al., Liquid Crystals 39(9), 2012, 1 141 -1 148). The LC medium with negative dielectric anisotropy shows a more favourable director orientation that has less tilt and more twist orientation compared to the LC medium with positive dielectric anisotropy, as a result of which these displays have a higher transmission. Further LC display modes, which are also used, in particular, for small and medium-sized LC displays for use in portable devices, such as, for example, tablet PCs or so-called smartphones, are the IPS mode and the FFS (fringe field switching) mode, in which LC media having positive dielectric anisotropy are used. The prior art discloses that the properties of a liquid- crystal display of the FFS type can be improved by adding liquid-crystal materials having negative dielectric anisotropy to highly polar LC media having positive dielectric anisotropy, causing the dielectric constant εΐ perpendicular to the longitudinal molecular axes of the LC mixture to be increased (see EP 2 628 779 A2). Consequently, the high negative dielectric anisotropy of the admixed substances must be compensated again by a higher proportion of materials having positive dielectric anisotropy in order to produce the polarity of the mixture which is necessary for switch- ing. There is therefore a need for LC mixture components which, although having a high ε±, reduce the polarity of an LC mixture having positive Δε to a lesser extent owing to a relatively low Δε. In other words, the ratio of εΐ to |Δε| must be as large as possible.

In JP(A) H10-236992 the following compound having negative dielectric anisotropy is described:

In CN106699710 compounds such as for example the following

are described.

The development in the area of liquid-crystalline materials is far from complete. In order to improve the properties of liquid-crystalline display elements, attempts are constantly being made to develop novel compounds which enable such displays to be optimised.

An object of the present invention is to provide compounds having advantageous properties for use in liquid-crystalline media. This object is achieved in accordance with the invention by the compounds of the general formula (I)

in which

W denotes O or S,

L¹ denotes R¹ or X¹ , denotes R² or X²,

R¹ , R² each, independently of one another, denote H, an alkyl or alkoxy radical having 1 to 15 C atoms, where, in addition, one or more CH₂ groups in these radicals may each be replaced, independentl of one another, by -C≡C- , -CH=CH-

, -O-, -S-, -CF₂O-, -OCF₂-, -CO-O- or -O-CO- in such a way that O- or S-atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by CN or halogen,

X¹ and X² independently of one another, denote halogenated alkyl, halogenated alkoxy, halogenated alkenyl or halogenated alkenyloxy, each having up to 5 C atoms, F, CI, CN, SCN, SF₅, preferably F, CH₂F, CF₂H, CF₃, OCF₂H, OCF₃, -OCH=CF₂ or -OCF=CF₂, particularly preferably F, CF₃ or OCF_3j

A¹ and A² each, independently of one another, denote a radical selected from the following groups: a) the group consisting of trans-1 ,4-cyclohexylene, 1 ,4- cyclohexenylene, and decaline-2,6-diyl, in which one or more non-adjacent CH₂ groups may be replaced by -O- and/or -S- and in which one or more H atoms may be replaced by F, b) the group consisting of 1 ,4-phenylene and 2,6- naphthylene, in which one or two CH groups may be replaced by N and in which, in addition, one or more H atoms may be replaced by L, c) the group consisting of cyclopentane-1 ,3-diyl, cyclopent- 2-ene-1 ,3-diyl, 1 ,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl, cyclobutane-1 ,3-diyl, thiophene-2,5-diyl, selenophene-2,5-diyl, and 1 ,2,3,4-tetrahydronanaphthaline-2,6-diyl, each of which may be mono- or polysubstituted by L, d) the group consisting of bicyclo[1 .1 .1 ]pentane-1 ,3-diyl, bicyclo[2.2.2]octane-1 ,4-diyl, and spiro[3.3]heptane-2,6-diyl, in which one or more H atoms may be replaced by F each, identically or differently, denote halogen, cyano, alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl group with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or CI,

Z¹ and Z² independently of one another, denote a single bond, -CF₂O-,

-OCF₂-, -CH₂CH₂-, -CF₂CF₂-, -C(O)O-, -OC(O)-, -CH₂O-, -OCH₂-, -CF=CH-, -CH=CF-, -CF=CF-, -CH=CH- or -C≡C-, preferably -CH₂O-, -OCH₂-, -CH₂CH₂- or a single bond, particularly preferably a single bond.

Y¹ , Y²,

Y³ and Y⁴ independently of one another, denote H, F, CI, CN, CF₃ or

OCF3, preferably H or F, m and n are, independently of one another, 0, 1 or 2, while m + n is 0,

1 or 2, with the proviso that at least one of Y¹ , Y², Y³ and Y⁴ is different from F and that at least one of Y¹ , Y², Y³ and Y⁴ is different from H.

A further object of the present invention is to provide liquid-crystalline media, in particular for use in VA, IPS or FFS displays.

This object is achieved in accordance with the invention by the provision of compounds of formula I.

In formula I, W preferably denotes O.

In another preferred embodiment, W in formula I denotes S.

In a preferred embodiment, in formula I or its subformulae below, one of Y¹ , Y², Y³ and Y⁴ denotes H.

In a particularly preferred embodiment, in formula I or its subformulae below, Y¹ denotes H and Y², Y³ and Y⁴ all denote F.

In another particularly preferred embodiment, in formula I or its subformulae below, Y² denotes H and Y¹ , Y³ and Y⁴ all denote F. In another particularly preferred embodiment, in formula I or its subformulae below, Y³ denotes H and Y¹, Y² and Y⁴ all denote F.

In yet another particularly preferred embodiment, in formula I or its subformulae below, Y⁴ denotes H and Y¹, Y² and Y³ all denote F. 1 In a preferred embodiment, in formula I or its subformulae below, two of Y ,

Y², Y³ and Y⁴ denote H.

In a particularly preferred embodiment, in formula I or its subformulae below,

Y¹ and Y² both denote H and Y³ and Y⁴ both denote F.

In a particularly preferred embodiment, in formula I or its subformulae below,

Y¹ and Y² both denote F and Y³ and Y⁴ both denote H.

In a particularly preferred embodiment, in formula I or its subformulae below,

Y¹ and Y⁴ both denote F and Y² and Y³ both denote H.

In a particularly preferred embodiment, in formula I or its subformulae below,

Y¹ and Y⁴ both denote H and Y² and Y³ both denote F.

The compounds of the formula I are preferably selected from the group of compounds of the formulae IA, IB, IC and ID

IB

wherein R¹, R², A¹, Z¹, X², Y¹, Y², Y³ and Y⁴have the meanings given above for formula I and preferably

R¹, R² each, independently of one another, denote straight chain alkyl, alkenyl or alkoxy with up to 7 C atoms, or cyclopropyl, cyclobutyl, cyclopentyl or cyclopen-1 -enyl, each, independently of one another, denote F, CF₃ or OCF₃,

A¹ denotes a radical selected from the following groups:

and Z¹ -CH2O-, -OCH2-, -CH2CH2- or a single bond, particularly preferably -CH₂O- or a single bond, m is O or l .

In a first preferred embodiment, the compounds of formula I are selected from the group of compounds of the formulae IA and IC. In a second preferred embodiment, the compounds of formula I are selected from the group of compounds of the formulae IB and ID.

Preferred compounds of formula IA are selected from the following sub- formulae IA-1 to IA-10:

IA-3



in which

R¹, R² and Z¹ have the meanings indicated above for formula IA.

Particularly preferred compounds of the formulae IA-1 to IA-10 are the compounds of the formula IA-1 and IA-3.

Preferred compounds of the formula IA-1 are compounds of the following formulae:

in which

R¹ and R² have the meanings indicated above for formula IA.

Preferred compounds of the formula IA-2 are compounds of the following formulae:

in which

R¹, R² and Z have the meanings indicated above for formula IA.

Preferred compounds of the formula IA-3 are compounds of the following formulae: IA-3-1

in which R¹ , R² and Z¹ have the meanings indicated above for formula IA and Z¹ preferably denotes -CH₂O-.

Preferred compounds of the formula IA-4 are compounds of the following

in which

R¹, R² and Z¹ have the meanings indicated above for formula IA.

Preferred compounds of the formula IA-5 are compounds of the following formulae:

IA-5-3

in which

R¹, R² and Z¹ have the meanings indicated above for formula IA.

Preferred compounds of the formula IA-6 are compounds of the following formulae:

IA-6-1

in which

R¹ , R² and Z¹ have the meanings indicated above for formula IA.

Preferred compounds of the formula IA-8 are compounds of the following formulae:

IA-8-4

in which

R¹, R² and Z¹ have the meanings indicated above for formula IA.

Preferred compounds of the formula IA-9 are compounds of the following formulae:

in which

R¹, R² and Z¹ have the meanings indicated above for formula IA.

Preferred compounds of the formula IA-10 are compounds of the following formulae:

10

35

in which

R¹ , R² and Z¹ have the meanings indicated above for formula IA.

Preferred compounds of formula IB-1 are selected from the following sub- formulae IB-1 to IB-12:

IB-4

in which R¹, X² and Z¹ have the meanings indicated above for formula IB.

Particularly preferred compounds of the formulae IB-1 to IB-10 are the compounds of the formula IB-1 .

Preferred compounds of the formula IB-1 are compounds of the following formulae:

IB-1 -5

in which

R¹ and X² have the meanings indicated above for formula IB.

Preferred compounds of the formula IB-2 are compounds of the following formulae:

IB-2-4

in which

R¹, X² and Z¹ have the meanings indicated above for formula IB. Preferred compounds of the formula IB-3 are compounds of the following formulae:

IB-3-2

Preferred compounds of the formula IB-4 are compounds of the following formulae:



in which

R¹, X² and Z¹ have the meanings indicated above for formula IB.

Preferred compounds of the formula IB-5 are compounds of the following formulae:

in which

R¹, X² and Z¹ have the meanings indicated above for formula IB. Preferred compounds of the formula IB-6 are compounds of the following formulae:

IB-6-2

in which

R¹, X² and Z¹ have the meanings indicated above for formula IB.

Preferred compounds of the formula IB-7 are compounds of the following formulae:



in which

R¹, X² and Z¹ have the meanings indicated above for formula IB.

Preferred compounds of the formula IB-8 are compounds of the following formulae:

in which

R¹, X² and Z¹ have the meanings indicated above for formula IB.

Preferred compounds of the formula IB-9 are compounds of the following formulae:

in which

R¹, X² and Z¹ have the meanings indicated above for formula IB.

Preferred compounds of the formula IB-10 are compounds of the following formulae:

in which

R¹, X² and Z¹ have the meanings indicated above for formula IB.

Preferred compounds of formula IC-1 are selected from the following sub- formulae IC-1 to IC-10:

IC-4

Particularly preferred compounds of the formulae IC-1 to IC-12 are the compounds of the formulae IC-1 and IC-3.

Preferred compounds of the formula IC-1 are compounds of the following formulae:

IC-1 -5

in which

R¹ and R² have the meanings indicated above for formula IC.

Preferred compounds of the formula IC-2 are compounds of the following formulae:

IC-2-4

in which

R¹, R² and Z¹ have the meanings indicated above for formula IC. Preferred compounds of the formula IC-3 are compounds of the following formulae:

Preferred compounds of the formula IC-4 are compounds of the following formulae:

in which

R¹, R² and Z¹ have the meanings indicated above for formula IC.

Preferred compounds of the formula IC-5 are compounds of the following formulae:

in which

R¹, R² and Z¹ have the meanings indicated above for formula IC. Preferred compounds of the formula IC-6 are compounds of the following formulae:

IC-6-2

in which

R¹, R² and Z¹ have the meanings indicated above for formula IC.

Preferred compounds of the formula IC-7 are compounds of the following formulae:

in which

R¹, R² and Z¹ have the meanings indicated above for formula IC.

Preferred compounds of the formula IC-8 are compounds of the following formulae:

IC-8-4

in which

R¹, R² and Z¹ have the meanings indicated above for formula IC.

Preferred compounds of the formula IC-9 are compounds of the following formulae:

in which

R¹, R² and Z¹ have the meanings indicated above for formula IC.

Preferred compounds of the formula IC-10 are compounds of the following formulae:

in which

R¹, R² and Z¹ have the meanings indicated above for formula IC.

Preferred compounds of formula ID-1 are selected from the following sub- formulae ID-1 to ID-12:

ID-4

Particularly preferred compounds of the formulae ID-1 to ID-10 are the compounds of the formula ID-1 .

Preferred compounds of the formula ID-1 are compounds of the following formulae:

ID-1 -5

in which

R¹ and X² have the meanings indicated above for formula ID.

Preferred compounds of the formula ID-2 are compounds of the following formulae:

ID-2-4

in which

R¹, X² and Z¹ have the meanings indicated above for formula ID.

Preferred compounds of the formula ID-3 are compounds of the following formulae:

ID-3-2

Preferred compounds of the formula ID-4 are compounds of the following formulae:

in which

R¹, X² and Z¹ have the meanings indicated above for formula ID.

Preferred compounds of the formula ID-5 are compounds of the following formulae:

ID-5-4

in which

R¹, X² and Z¹ have the meanings indicated above for formula ID. Preferred compounds of the formula ID-6 are compounds of the following formulae:

ID-6-2

in which

R¹, X² and Z¹ have the meanings indicated above for formula ID.

Preferred compounds of the formula ID-7 are compounds of the following formulae:

in which

R¹, X² and Z¹ have the meanings indicated above for formula ID.

Preferred compounds of the formula ID-8 are compounds of the following formulae:

ID-8-4

in which

R¹, X² and Z¹ have the meanings indicated above for formula ID.

Preferred compounds of the formula ID-9 are compounds of the following formulae:

in which

R¹, X² and Z¹ have the meanings indicated above for formula ID.

Preferred compounds of the formula ID-10 are compounds of the following formulae:

35

in which

R¹, X² and Z¹ have the meanings indicated above for formula ID.

The compounds of formula IA and IC according to the invention all have negative Δε and are therefore suitable, in particular, for use in VA-TFT displays, and in IPS- and FFS displays. The compounds according to the invention preferably have a Δε of < -2.5, preferably of < -5 and particularly preferably a Δε of < -8. They exhibit very good compatibility with the conventional substances used in liquid-crystal mixtures for displays.

The compounds of formula IB and ID according to the invention have dielectric properties particularly well suitable for application in LC media for IPS or FFS displays due to the high values of their dielectric ratio (ε± / Δε).

For the present invention

denote trans-1 ,4-cyclohexylene

denote 1 ,4-phenylene.

Halogen is F, CI, Br and I.

If R¹ or R² is an alkyl radical and/or an alkoxy radical, this can be straight- chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy.

R¹ and R² may each, independently of one another, be an alkenyl radical having from 2 to 15 carbon atoms, which may be straight-chain or branched. It is preferably straight-chain and has from 2 to 7 carbon atoms. Accordingly, it is preferably vinyl, prop-1 - or -2-enyl, but-1 -, -2- or -3-enyl, pent-1 -, -2-, -3- or -4-enyl, hex-1 -, -2-, -3-, -4- or -5-enyl, or hept-1 -, -2-, -3-, -4-, -5- or -6-enyl.

R¹ and R² may each, independently of one another, be oxaalkyi, preferably straight-chain 2-oxapropyl (= methoxymethyl), 2-oxabutyl (= ethoxymethyl) or 3-oxabutyl (= methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or

5-oxahexyl, or 2-, 3-, 4-, 5- or 6-oxaheptyl.

R¹ and R² may each, independently of one another, be an alkyl radical having from 1 to 15 carbon atoms in which one CH₂ group has been replaced by -O- and one has been replaced by -CO-, where these are preferably adjacent. This thus contains an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. This is preferably straight-chain and has from 2 to 6 carbon atoms.

R¹ and R² may each, independently of one another, be an alkyl radical having from 1 to 15 carbon atoms in which one CH₂ group has been replaced by unsubstituted or substituted -CH=CH- and an adjacent CH₂ group has been replaced by CO or CO-O or O-CO, where this may be straight-chain or branched. It is preferably straight-chain and has from 4 to 13 carbon atoms. R¹ and R² may each, independently of one another, be an alkyl radical having from 1 to 15 carbon atoms or alkenyl radical having from 2 to 15 carbon atoms, each of which is monosubstituted by -CN or -CF₃ and is preferably straight-chain. The substitution by -CN or -CF₃ is possible in any desired position.

R¹ and R² may each, independently of one another, be an alkyl radical in which two or more CH₂ groups have been replaced by -O- and/or -CO-O-, where this may be straight-chain or branched. It is preferably branched and has from 3 to 12 carbon atoms.

R¹ and R² may each, independently of one another, be an alkyl radical having from 1 to 15 carbon atoms or an alkenyl radical having from 2 to 15 carbon atoms, each of which is at least monosubstituted, preferably monosubstituted, by halogen, where these radicals are preferably straight- chain and halogen is preferably -F or -CI. The resultant radicals exclude perfluorinated radicals, such as -CF₃. In the case of monosubstitution, the fluorine or chlorine substituent can be in any desired position, but is preferably in the co-position.

R¹ or R² may be an alkyl or alkoxy radical having 1 to 15 C atoms, preferably 1 to 5, particularly preferably 1 , where one or more CH₂ groups, preferably one, in these radicals ma each be replaced independently of one another by

. R is preferably cyclopropyl cyclopropylmethyl, cyclobutyl, cyclobutylmethyl, cyclopentylmethyl, cyclopent-1 -enyl or cyclopent-1 -enylmethyl.

In case X¹ and X², independently of one another, denote an halogenated alkyl, halogenated alkoxy, halogenated alkenyl or halogenated alkenyloxy, each having up to 5 C atoms, this can be straight chain or branched, preferably straight chain. Preferably, halogen is CI or F, particularly preferably F. Preferably, the groups are perfluorinated, such as -CF₃ and - C₂F₅.

The compounds of the general formula I are prepared by methods known per se, as described in the literature (for example in the standard works, such as Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and are suitable for the said reactions. Use can be made here of variants which are known per se, but are not mentioned here in greater detail. If desired, the starting materials can also be formed in situ by not isolating them from the reaction mixture, but instead immediately converting them further into the compounds of the general formula I

Preferred synthetic pathways towards compounds according to the invention is shown in the schemes below and is further illustrated by means of the working examples. The syntheses can be adapted to the particular desired compounds of the general formula I by choice of suitable starting materials.

The compounds of formula I are preferably synthesized as shown in schemes 1 to 3. In the schemes, the occurring groups are defined as indicated above for formula I and alkyl denotes straight chain alkyl or (alkylcycloalkyl)alkyl, preferably (alkylcycloalkyl)methyl, having up to 15 C atoms.

Bromodifluorobenzene derivatives 1 can be ortho-metallated with e.g. LDA to give a phenyl lithium intermediate which then reacts with iodine to give compounds 2 (scheme 1 ). Suitably substituted benzene boronic acids (3) then react selectively with the iodine in 2 in Suzuki reactions, e.g. in the presence of Pd(PPh₃)₂Cl2 and NaBO2 as a base. The bromine atom in 4 can be substituted using thiophenol in the presence of Pd2(dba)3,

XanthPhos and KOtBu to give thioethers (5). The latter undergo ring closure, catalysed by Pd(OAc)₂ / 2,6-Me₂PhCOOH to give

dibenzothiophenes 6.

Scheme 1 :

From Bromides 4 the phenols 7 can be obtained, e.g. by palladium catalysed treatment with aq. potassium hydroxide. These phenols (7, scheme 2) undergo ring closure by treatment with a base, e.g. K₃PO₄ in DMPU, to yield dibenzofurans. Alternatively, the phenols 7 can be reacted via the corresponding triflates (TfO, 9) to dibenzothiophenes 6 in analogy to the process described in EP 3085753 A1 .

6 8

Preferred compounds of formula I are prepared according to scheme 3 where commercially available 2-bromo-4-fluoro-5-nitro-phenol is first protected, e.g. by benzylation, and then reacted in a Suzuki coupling with a difluorobenzene boronic acid to give nitrobiphenyls 13. The nitro group is reduced and the resulting phenyl aniline (14) transferred into a phenol (15) by diazotation and nucleophilic hydroxylation following standard

procedures. The phenols 15 are alkylated and then deprotected to give phenols 17 which are transferred to compounds of formula I (18, 19) according to the procedures shown in schemes 1 and 2.

Scheme 3:

reduction

deprotection

see Schemes 1 , 2

Another object of the invention are compounds of formula II

in which the occurring groups and parameters have the meanings indicated above for formula I, and

R" denotes alkyl having 1 to 5 C atoms, preferably methyl, or phenyl in which one or two CH groups may be replaced by N and one or more H atoms may be replaced by halogen or alkyl having 1 to 10 C atoms, and their use as intermediates in the synthesis of compounds of formula I. Compounds of formula II can be reacted according to M. Tobisu et al., Chem. Sci., 2016, 7, 2587-2591 , in an intramolecular cyclisation to compounds of formula I.

Another object of the present invention is a process of the preparation of a compound of formula I by treatment of a compound of formula II with a palladium-catalyst in a solvent, preferably at a temperature in the range of from 100 °C to 150°C. The concentration of the catalyst is 1 to 20 mol%, preferably 5 to 15% based on the amount of the compound of formula II. Preferred catalyst is a palladium salt, preferably palladium(ll)acetate or palladium(ll)chloride, preferably in the presence of a ligand which is particularly preferably a carboxylic acid, very particularly preferably 2,6- dimethylbenzoic acid.

Preferred solvents are benzene, toluene, xylene, mesitylene, and the like.

The reactions described in the schemes above should only be regarded as illustrative. The person skilled in the art can carry out corresponding variations of the syntheses described and also follow other suitable synthetic routes in order to obtain compounds of the formula I.

As already mentioned, the compounds of the general formula I can be used in liquid-crystalline media.

The present invention therefore also relates to a liquid-crystalline medium comprising two or more liquid-crystalline compounds, comprising one or more compounds of the general formula I.

The present invention also relates to liquid-crystalline media comprising from 2 to 40, preferably from 4 to 30, components as further constituents besides one or more compounds of the formula I according to the invention. These media particularly preferably comprise from 7 to 25 components besides one or more compounds according to the invention. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of the azoxy- benzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl esters of cyclohexanecarboxylic acid, phenyl or cyclohexyl esters of cyclohexyl benzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexyl phenyl esters of benzoic acid, of cyclohexanecarboxylic acid or of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclo- hexanes, cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes, 1 ,4- biscyclohexylbenzenes, 4',4'-biscyclohexylbiphenyls, phenyl- or cyclohexyl- pyrimidines, phenyl- or cyclohexyl pyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1 ,3-dithianes, 1 ,2-diphenylethanes, 1 ,2-dicyclohexyl- ethanes, 1 -phenyl-2-cyclohexylethanes, 1 -cyclohexyl-2-(4-phenylcyclohexyl)- ethanes, 1 -cyclohexyl-2-biphenylylethanes, 1 -phenyl-2-cyclohexyl- phenylethanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids. The 1 ,4-phenylene groups in these compounds may also be fluorinated.

The most important compounds suitable as further constituents of media according to the invention can be characterised by the formulae (1 ), (2), (3),

(4) and (5):

R'-L-E-R" (1 )

R'-L-COO-E-R" (2)

R'-L-OOC-E-R" (3)

R'-L-CH₂CH₂-E-R" (4)

R'-L-CF₂O-E-R" (5)

In the formulae (1 ), (2), (3), (4) and (5), L and E, which may be identical or different, are each, independently of one another, a divalent radical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images, where Phe is unsubstituted or fluorine-substituted 1 ,4-phenylene, Cyc is trans-1 ,4-cyclohexylene or 1 ,4- cyclohexenylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1 ,3- dioxane-2,5-diyl, and G is 2-(trans-1 ,4-cyclohexyl)ethyl.

One of the radicals L and E is preferably Cyc or Phe. E is preferably Cyc,

Phe or Phe-Cyc. The media according to the invention preferably comprise one or more components selected from the compounds of the formulae (1 ), (2), (3), (4) and (5) in which L and E are selected from the group consisting of Cyc and Phe and simultaneously one or more components selected from the compounds of the formulae (1 ), (2), (3), (4) and (5) in which one of the radicals L and E is selected from the group consisting of Cyc and Phe and the other radical is selected from the group consisting of -Phe-Phe-,

-Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more com- ponents selected from the compounds of the formulae (1 ), (2), (3), (4) and (5) in which the radicals L and E are selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-. In a smaller sub-group of the compounds of the formulae (1 ), (2), (3), (4) and (5), R' and R" are each, independently of one another, alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. This smaller sub-group is called group A below, and the compounds are referred to by the sub-formulae (1 a), (2a), (3a), (4a) and (5a). In most of these com- pounds, R' and R" are different from one another, one of these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller sub-group of the compounds of the formulae (1 ), (2), (3), (4) and (5), which is known as group B, E is

In the compounds of group B, which are referred to by the sub-formulae (1 b), (2b), (3b), (4b) and (5b), R' and R" are as defined for the compounds of the sub-formulae (1 a) to (5a) and are preferably alkyl, alkenyl, alkoxy or alkoxy- alkyl.

In a further smaller sub-group of the compounds of the formulae (1 ), (2), (3), (4) and (5), R" is -CN. This sub-group is referred to below as group C, and the compounds of this sub-group are correspondingly described by sub- formulae (1 c), (2c), (3c), (4c) and (5c). In the compounds of the sub- formulae (1 c), (2c), (3c), (4c) and (5c), R' is as defined for the compounds of the sub-formulae (1 a) to (5a) and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.

Besides the preferred compounds of groups A, B and C, other compounds of the formulae (1 ), (2), (3), (4) and (5) having other variants of the proposed substituents are also customary. All these substances are obtainable by methods which are known from the literature or analogously thereto.

Besides the compounds of the general formula I according to the invention, the media according to the invention preferably comprise one or more compounds selected from groups A, B and/or C. The proportions by weight of the compounds from these groups in the media according to the invention are: group A: from 0 to 90%, preferably from 20 to 90%, in particular from 30 to

90%

group B: from 0 to 80%, preferably from 10 to 80%, in particular from 10 to

70%

group C: from 0 to 80%, preferably from 5 to 80%, in particular from 5 to

50%. The media according to the invention preferably comprise from 1 to 40%, particularly preferably from 5 to 30%, of the compounds of the formula I according to the invention. Preference is furthermore given to media comprising more than 40%, in particular from 45 to 90%, of compounds of the formulae formula I according to the invention. The media preferably comprise three, four or five compounds of the formula I according to the invention.

Examples of the compounds of the formulae (1 ), (2), (3), (4) and (5) are the compounds listed below:

where R¹ and R², independently of one another, are -C_nH_2n+i or -OC_nH₂n+i , and n = 1 to 8, and L¹ and L², independently of one another, are -H or -F,

where m and n, independently of one another, are from 1 to 8.

The media according to the invention are prepared in a manner conventional per se. In general, the components are dissolved in one another, advantageously at elevated temperature. By means of suitable additives, the liquid-crystalline phases of the present invention can be modified in such a way that they can be used in all types of liquid-crystal display ele- ments that have been disclosed hitherto. Additives of this type are known to the person skilled in the art and are described in detail in the literature (H. Kelker/R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Wein- heim, 1980). For example, pleochroic dyes can be used for the preparation of coloured guest-host systems or substances can be added in order to modify the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases.

The present invention also relates to electro-optical liquid-crystal display elements containing a liquid-crystalline medium according to the invention.

The invention is explained in greater detail below with reference to working examples, but without being restricted thereby.

Above and below, Δη denotes the optical anisotropy (589 nm, 20°C) and Δε denotes the dielectric anisotropy (1 kHz, 20°C). The Δε and Δη values of the compounds according to the invention are obtained by extrapolation from liquid-crystalline mixtures consisting of 10% of the respective compound according to the invention and 90% of the commercially available liquid-crystal mixture ZLI-2857 (for As) or ZLI-4792 (for An) (Merck KGaA, Darmstadt). In cases of limited solubility, the com- pound is measured in a mixture comprising only 5% of the compound, which is noted by the addition (5%) after the values in question.

The solubility is measured by quantitative HPTLC using HPTLC silica RP18 F254 plates (Article No. 1 .16225, 10x20cm, Merck KGaA,

Darmstadt, Germany) and Methanol/2-Methyltetrahydrofuran 80/20 (v/v) as eluent. The migration distance is 5cm and peaks are detected using a TLC scanner (Camag Chemie-Erzeugnisse und Adsorptionstechnik AG & Co. GmbH) by UV irradiation at a wavelength of 254nm. The quantitative measurement is performed by integration of the peak intensity and comparison with a calibration curve.

For the calibration curve, a stock solution of a sample of approx. 6mg in 20ml of 2-methyltetrahydrofuran is prepared and 1 ml of this solution is diluted with 50 ml of 2-methyltetrahydrofuran. Standards of 1 , 3, 6, 10, 15,

20, 25 and 30 μΙ, respectively, are applied to the TLC plate, the TLC is developed and the peak intensity determined.

Two 25mg samples of the compound to be analysed in 0.5 ml each in a given solvent are prepared by shaking for 24h at 25°C and 600 rpm. If the solution is clear, more substance is added until a saturated solution is obtained.

After cooling to room temperature the samples are filtered through a syringe filter (pore size 0.2μηη) The solutions are stored in glass vials for 7 d at room temperature and the solubility is determined by HPTLC that day and again after additional 7 d using 20, 23 and 25μΙ of the solution, respectively as described for the standards.

Abbreviations

BuLi n-butyllithium

LDA lithiumdiisopropylamide

DIPA diisopropylamin

THF tetrahydrofuran

DMSO dimethylsulfoxide

DIPA diisopropylamine

MTB ether methyl tert. -butyl ether

m.p. melting point Examples

Comparative Example 1

Step 1 : 1 -bromo-5-butoxy-3,4-difluoro-2-iodo-benzene

A solution of 5-bromo-1 -butoxy-2,3-difluoro-benzene (19.5 g, 74 mmol) in THF (40 ml_) is added dropwise to a freshly prepared LDA solution (12.4 ml_ DIPA, 120 ml_ THF and 55 ml_ BuLi (15% in hexane)) at -70 °C. The reaction is allowed to warm up to -45°C and stirred for 2h before it is cooled down again (-70 °C) and treated with a solution of iodine (22.4g, 88.2 mmol) in THF (40 ml_). The reaction mixture is stirred for 1 h at the same temperature, slowly warmed up to 0°C and treated subsequently with water (50 ml_), 25% HCI (until pH = 5-6) and ethyl acetate. The aqueous phase is separated and extracted with ethyl acetate. The combined organic phase is washed with aq. NaHSO3 (sat.), aq. NaCI (sat.), dried over Na₂SO₄ and concentrated in vacuo. The residue is filtered through silica to give 1 -bromo-5-butoxy-3,4-difluoro-2-iodo-benzene as a colourless oil.

Step 2: 1 -bromo-5-butoxy-2-(4-ethoxy-2,3-difluoro-phenyl)-3,4-difluoro- benzene

A solution of 4-ethoxy-2,3-difluoro boronic acid (1 1 .4 g, 56.4 mmol) and 1 - bromo-5-butoxy-3,4-difluoro-2-iodo-benzene (22.1 g, 56.4 mmol) in THF (180 mL) is treated with solution of sodium metaborate (12.6 g, 45 mmol) in water (70 mL) at room temperature. The resulting mixture is degassed and treated with Pd(PPh₃)₂Cl₂ (0.84 g, 1 .17 mmol) and hydrazine hydroxide (0.08 mL, 1 .72 mmol). The reaction mixture is stirred overnight at 70 °C, two phases were separated and aqueous one is extracted with methyl tert- butyl ether. The combined organic phase is washed with aq. NaCI (sat.), dried over Na₂SO₄ and concentrated in vacuo. The residue (23 g) is purified by flash chromatography (heptane/ethyl acetate) to give 1 -bromo- 5-butoxy-2-(4-ethoxy-2,3-difluoro-phenyl)-3,4-difluoro-benzene as colourless crystals.

Step 3: 1 -butoxy-4-(4-ethoxy-2,3-difluoro-phenyl)-2,3-difluoro-5- phenylsulfanyl-benzene

A degassed solution of thiophenol (1 .2 g, 10.7 mmol), 1 -bromo-5-butoxy-2- (4-ethoxy-2,3-difluoro-phenyl)-3,4-difluoro-benzene (4.1 g, 9.73 mmol) and

KOfBu (1 .31 g, 1 1 .68 mmol) in toluene (40 mL) is treated with solution of Pd₂(dba)₃ (92 mg, 0.10 mmol) and XanPhos (128 mg, 0.21 mmol) in toluene (2 mL) at room temperature under argon atmosphere. The resulting mixture is stirred overnight at 1 10 °C before it is diluted with ethyl acetate, washed with aq. NaHCO₃(sat.) and water, dried over Na₂SO₄, filtered and concentrated under reduced pressure. The residue is purified by flash chromatography (heptane/ethyl acetate) to give 1 -butoxy-4-(4- ethoxy-2,3-difluoro-phenyl)-2,3-difluoro-5-phenylsulfanyl-benzene as a yellowish oil. Step 4: 3-butoxy-7-ethoxy-1 ,2,8,9-tetrafluoro-dibenzothiophene

Palladium acetate (170 mg, 0.73 mmol) and 2,6-dimethylbenzoic acid (250 mg, 2.20 mmol) were added to a degassed solution of 1 -butoxy-4-(4- ethoxy-2,3-difluoro-phenyl)-2,3-difluoro-5-phenylsulfanyl-benzene (2.2g, 4.88 mmol) in toluene (20 ml_) at room temperature. The resulting mixture is stirred overnight at 1 10°C before it is diluted with ethyl acetate and washed with aq. NaHCO3(sat.) and water, dried over Na₂SO₄, filtered and concentrated under reduced pressure. The residue is purified by

chromatography and recrystallization from acetonitrile to afford 3-butoxy-7- ethoxy-1 ,2,8,9-tetrafluoro-dibenzothiophene as colourless crystals, m.p. 143°C.

¹H NMR: 1 .01 (app t, J = 7.4 Hz, 3H), 1 .61 - 1 .48 (m, 7H), 1 .86 (app dq, J = 8.6, 6.6 Hz, 2H), 4.1 1 (app t, J = 6.5 Hz, 2H), 4.18 (app q, J = 7.0 Hz, 2H), 7.06 (dd, J = 6.6, 2.2 Hz, 2H); ¹⁹F NMR: -161 .5 (m, 2F), -132.1 (m, 2F); EI-MS: 372.0

Comparative Example 2

In analogy to Comparative Example 1 , the following compound is prepared

¹H NMR: δ 7.33 (dd, J = 5.6, 1 .5 Hz, 1 H), 7.1 1 (dd, J = 6.4, 1 .7 Hz, 1 H), 3.93 (d, J = 6.4 Hz, 2H), 2.79 (td, J = 7.6, 1 .4 Hz, 2H), 2.01 - 1 .80 (m, 5H), 1.74 (h, J= 7.3 Hz, 2H), 1.42-1.18 (m, 5H), 1.13 (qd, J= 12.8, 3.3 Hz, 2H), 1.05-0.87 (m, 8H).¹⁹F NMR: δ -131.14 - -131.77 (m), -133.45- -134.10 (m), -147.67 (dd, J= 19.0, 5.6 Hz), -161.63. EI-MS: 452.1.

Phase sequence: K 153 I

Δε: -12.0

Δη: 0.1592

Clp: 118 °C

γι: 1319 mPa s

(all values extrapolated from 5% solution)

Comparative Example 3:

In analogy to Comparative Example 1, the following compound is prepared:

¹H NMR: δ 7.34 (dd, J =5.5, 1.5 Hz, 1H), 7.12 (dd, J = 6.4, 1.7 Hz, 1H), 4.15 (t, J = 6.5 Hz, 2H), 2.80 (td, J = 7.7, 1.4 Hz, 2H), 1.96 - 1.85 (m, 2H), 1.71 (dq, J = 9.7, 7.3 Hz, 2H), 1.62 - 1.53 (m, 2H), 1.39 (h, J = 3.6 Hz, 4H) 1.04 (t, J = 7.4 Hz, 3H), 0.94 (td, J = 7.2, 6.2, 3.4 Hz, 3H). EI-MS: 398.1

Comparative Example 4:

In analogy to Comparative Example 1 , the following compound is prepared

Examples

Example 1: 1 ,2,9-trifluoro-7-pentyl-3-propoxy-dibenzothiophene

Ste 1 : 1 -bromo-3,4-difluoro-2-iodo-5-propoxy-benzene

A solution of 5-bromo-1 ,2-difluoro-3-propoxy-benzene (29.0 g, 1 15.5 mmol) in THF (60 ml_) is added dropwise to a freshly prepared LDA solution (19.5 ml_ DIPA, 180 ml_ THF and 87 ml_ BuLi (15% in hexane)) at -70 °C. The reaction is allowed to warm up to -45°C and stirred for 2h before it is cooled down again (-70 °C) and treated with a solution of iodine (35.2g, 138.6 mmol) in THF (60 ml_). The reaction mixture is stirred for 1 h at the same temperature, slowly warmed up to 0°C and treated subsequently with water (100 ml_), 25% HCI (until pH = 5-6) and ethyl acetate. The aqueous phase is separated and extracted with ethyl acetate. The combined organic phase is washed with aq. NaHSO3 (sat.), aq. NaCI (sat.), dried over Na₂SO₄ and concentrated in vacuo. The residue is filtered through silica to give 1 -bromo-5-butoxy-3,4-difluoro-2-iodo-benzene as a colourless oil.

Step 2: 1 -bromo-3,4-difluoro-2-(2-fluoro-4-pentyl-phenyl)-5-propoxy- benzene

A solution of (2-fluoro-4-pentyl-phenyl)boronic acid (10.5 g, 50.0 mmol) and 1 -bromo-3,4-difluoro-2-iodo-5-propoxy-benzene (18.8 g, 50.0 mmol) in THF (150 ml_) is treated with solution of sodium metaborate (1 1 .1 g, 40 mmol) in water (65 mL) at room temperature. The resulting mixture is degassed and treated with Pd(PPh₃)₂Cl₂ (0.74 g, 1 .04 mmol) and hydrazine hydroxide (0.07 mL, 1 .53 mmol). The reaction mixture is stirred overnight at 70 °C, two phases were separated and aqueous one is extracted with methyl tert-butyl ether. The combined organic phase is washed with aq. NaCI (sat.), dried over Na₂SO₄ and concentrated in vacuo. The residue is purified by flash chromatography (heptane/ethyl acetate) to give 1 -bromo-3,4-difluoro-2-(2-fluoro-4-pentyl-phenyl)-5- propoxy-benzene as colourless crystals.

Step 3: 3,4-difluoro-2-(2-fluoro-4-pentyl-phenyl)-1 -phenylsulfanyl-5- propoxy-benzene

A degassed solution of thiophenol (0.92 g, 8.21 mmol), 1 -bromo-3,4- difluoro-2-(2-fluoro-4-pentyl-phenyl)-5-propoxy-benzene (4.1 g, 9.73 mmol) and KOfBu (1 .31 g, 1 1 .68 mmol) in toluene (36 mL) is treated with a solution of Pd₂(dba)₃ (140 mg, 0.15 mmol) and XanPhos (196 mg, 0.33 mmol) in toluene (2 mL) at room temperature under argon atmosphere. The resulting mixture is stirred overnight at 1 10 °C before it is diluted with ethyl acetate, washed with aq. NaHCOs(sat.) and water, dried over

Na₂SO₄, filtered and concentrated under reduced pressure. The residue is purified by flash chromatography (heptane/ethyl acetate) to give 3,4- difluoro-2-(2-fluoro-4-pentyl-phenyl)-1 -phenylsulfanyl-5-propoxy-benzene as a yellowish oil.

Step 4: 1 ,2,9-trifluoro-7-pentyl-3-propoxy-dibenzothiophene

Palladium acetate (1 .3 g, 5.54 mmol) and 2,6-dimethylbenzoic acid (1 .9 g,

16.6 mmol) are added to a degassed solution of 3,4-difluoro-2-(2-fluoro-4- pentyl-phenyl)-1 -phenylsulfanyl-5-propoxy-benzene (5.7 g, 12.3 mmol) in toluene (60 ml_) at room temperature. The resulting mixture is stirred overnight at 1 10°C before it is diluted with ethyl acetate and washed with aq. NaHCOs(sat.) and water, dried over Na2SO₄, filtered and concentrated under reduced pressure. The residue is purified by chromatography (heptane / chlorobutane) and recrystallization from acetonitrile to afford 1 ,2,9-trifluoro-7-pentyl-3-propoxy-dibenzothiophene as colourless crystals. ¹H NMR: δ 7.73 (dd, J = 7.0, 1 .8 Hz, 1 H), 7.16 (dd, J = 12.6, 1 .4 Hz, 1 H), 4.13 (t, J = 6.6 Hz, 2H), 3.31 (s, 2H), 2.76 - 2.64 (m, 2H), 2.51 (p, J = 1 .9 Hz, 3H), 1 .91 - 1 .74 (m, 2H), 1 .64 (p, J = 7.4 Hz, 2H), 1 .40 - 1 .23 (m, 4H), 1 .02 (t, J = 7.4 Hz, 3H), 0.87 (t, J = 6.9 Hz, 3H). ¹⁹F NMR: δ -108.38 (dd, J = 99.5, 12.7 Hz), -133.82 (ddd, J = 99.5, 19.5, 1 .8 Hz), -162.49 (dd, J = 19.7, 6.9 Hz). EI-MS: 366.1

Phase sequence: K 80 I

Δε: -7.3

Δη: 0.1513

Clp: 6 °C

γι : 188 mPa s

Example 2: 1 ,2,8-trifluoro-7-pentoxy-3-propoxy-dibenzothiophene

Step 1 : 1 -bromo-2-(2,5-difluoro-4-pentoxy-phenyl)-3,4-difluoro-5-propoxy- benzene

A solution of sodium metaborate octahydrate (1 .37 g, 4.96 mmol) in water (8 mL) is added to a stirred solution of 2-(2,5-difluoro-4-pentoxy-phenyl)- 4,4,5,5-tetramethyl-l ,3,2-dioxaborolane (2.0 g, 6.13 mmol) and 1 -bromo- 3,4-difluoro-2-iodo-5-propoxy-benzene (2.3 g, 6.13 mmol) at room temperature. The mixture is degassed for 20 min, before it is treated with bis(triphenylphosphine)palladium(ll) chloride (0.09 g, 0.13 mmol) and aqueous hydrazine (0.01 mL, 0.19 mmol). The reaction mixture is stirred under reflux for 4 h, aqueous phase is separated and extracted with methyl tert-butyl ether. The combined organic phase is washed with sat. NaCI solution, dried over Na₂SO₄, filtered and concentrated under reduced pressure. The residue is purified by chromatography (heptane / ethyl acetate) to afford 1 -bromo-2-(2,5-difluoro-4-pentoxy-phenyl)-3,4-difluoro-5- propoxy-benzene as a colourless oil.

Step 2: 2-(2,5-difluoro-4-pentoxy-phenyl)-3,4-difluoro-5-propoxy-phenol

A solution of potassium hydroxide (2.6 g, 46.7 mmol) in water (30 mL) is added to a stirred solution of 1 -bromo-2-(2,5-difluoro-4-pentoxy-phenyl)- 3,4-difluoro-5-propoxy-benzene (14.0 g, 23.3 mmol) in 1 ,4-dioxane (60 mL) at room temperature. The mixture is degassed for 30 min, before it is treated with bis(dibenylideneacetone)palladiunn (0.67 g, 1 .17 mmol) and tert-BuXPhos (0.79 g, 1 .87 mmol). The reaction mixture is stirred for 6 h at 90 °C, quenched with aqueous hydrochloric acid (2M). The aqueous phase is separated and extracted with ethyl acetate. The combined organic phase is washed with sat. NaCI solution, dried over Na₂SO₄, filtered and concentrated under reduced pressure. The residue is purified by

chromatography (heptane / ethyl acetate) to afford 2-(2,5-difluoro-4- pentoxy-phenyl)-3,4-difluoro-5-propoxy-phenol as a colourless oil.

Step 3: [2-(2,5-difluoro-4-pentoxy-phenyl)-3,4-difluoro-5-propoxy-ph trifluoromethanesulfonate

Trifluoromethanesulfonic anhydride (2.9 mL, 17.7 mmol) is added dropwise to a stirred solution of 2-(2,5-difluoro-4-pentoxy-phenyl)-3,4-difluoro-5- propoxy-phenol (5.7 g, 14.7 mmol), triethylamine (3.1 mL, 22.0 mmol) and 4-(dimethylamino)-pyridine (54 mg, 0.44 mmol) in dichloromethane (50 mL) at 10°C. The resulting mixture is stirred overnight at room temperature, filtered through a short pad of silica (eluent: chlorobutane) and

concentrated under reduced pressure. The residue is purified by

chromatography (heptane / chlorobutane) to afford [2-(2,5-difluoro-4- pentoxy-phenyl)-3,4-difluoro-5-propoxy-phenyl] trifluoromethanesulfonate as a colourless oil.

Step 4: 1 ,2,8-trifluoro-7-pentoxy-3-propoxy-dibenzothiophene o=s^"

Ν,Ν-diisopropylethylamine (3.0 mL, 17.9 mmol) is added to a stirred solution of [2-(2,5-difluoro-4-pentoxy-phenyl)-3,4-difluoro-5-propoxy- phenyl] trifluoromethanesulfonate (5.9 g, 1 1 .4 mmol) and 3- mercaptopropionic acid 2-ethyl-hexyl ester (3.5 mL, 14.9 mmol) in toluene (30 mL). The mixture is degassed for 1 h, before it is treated with

Tris(dibenzylideneacetone)dipalladium(0) (1 10 mg, 0.1 1 mmol) and (Oxydi- 2,1 -phenylene)bis(diphenylphosphine) (125 mg, 0.23 mmol). The reaction mixture is stirred overnight at 1 10 °C, slowly treated with a solution of potassium tert-butylate (2.67 g, 23.7 mmol) in THF (15 mL). The resulting mixture is stirred for two days at 1 10 °C, cooled to the ambient

temperature, treated with methyl tert-butyl ether and water. The aqueous phase is separated and extracted with methyl tert-butyl ether. The combined organic phase is washed with sat. NaCI solution, dried over Na2SO₄, filtered and concentrated under reduced pressure. The residue is purified by chromatography (heptane / chlorobutane) and recrystallization from acetonitrile to afford 1 ,2,8-trifluoro-7-pentoxy-3-propoxy- dibenzothiophene as colourless crystals. ¹H NMR: δ 7.89 (d, J = 1 1 .5 Hz, 1 H), 7.35 - 7.23 (m, 1 H), 7.07 (dd, J = 6.2, 1 .8 Hz, 1 H), 4.07 (dt, J = 1 1 .7, 6.6 Hz, 4H), 1 .98 - 1 .80 (m, 4H), 1 .54 - 1 .36 (m, 4H), 1 .08 (t, J = 7.4 Hz, 3H), 0.95 (t, J = 7.1 Hz, 3H). ¹⁹F NMR: δ -136.34 (dd, J = 1 1 .5, 7.7 Hz), - 144.15 (dd, J = 19.3, 2.0 Hz), -162.90 (dd, J = 19.3, 6.3 Hz). EI-MS: 382.0. Phase sequence: K 126 I

Δε: -10.1

Δη: 0.1455

Clp: 13.8 °C

γι : 342 mPa s (all values extrapolated from 5% solution)

Example 3:

In analogy to Example 2, the following compound is prepared:

¹H NMR: δ 7.88 (d, J = 10.5 Hz, 1 H), 7.55 (d, J = 6.6 Hz, 1 H), 7.1 1 (dd, J 6.3, 1 .8 Hz, 1 H), 4.08 (t, J = 6.6 Hz, 2H), 2.75 (t, J = 7.6 Hz, 2H), 2.01 - 1 .81 (m, 2H), 1 .68 (p, J = 7.3 Hz, 2H), 1 .37 (h, J = 3.6 Hz, 4H), 1 .09 (t, J = 7.4 Hz, 3H), 0.95 - 0.84 (m, 3H). ¹⁹F NMR: δ -122.25 (dd, J = 10.6, 6.6 Hz), -143.02 (d, J = 19.2 Hz), -162.95 (d, J = 25.2 Hz). EI-MS: 366.2 Phase sequence: K 107 I

Δε: -6.5

Δη: 0.1372

Clp: -19.8 °C

γι : 188 mPa s

(all values extrapolated from 5% solution)

Example 4:

In analo to Example 1 , the following compound is prepared:

¹H NMR (Chloroform-c/) δ 7.33 (s, 1 H), 7.07 (dd, J = 6.5, 1 .6 Hz, 1 H), 6.96 (d, J = 12.1 Hz, 1 H), 3.89 (d, J = 6.4 Hz, 2H), 2.70 (t, J = 7.7 Hz, 2H), 1 .94 (dd, J = 13.3, 3.4 Hz, 2H), 1 .83 (ddd, J = 14.1 , 8.1 , 4.9 Hz, 3H), 1 .67 (p, J = 7.3 Hz, 2H), 1 .41 - 0.81 (m, 19H). ¹⁹F NMR: δ -107.49 (dd, J = 102.1 , 12.1 Hz), -132.18 (dd, J = 102.0, 18.3 Hz), -161 .84 (dd, J = 18.6, 6.5 Hz). EI- MS: 462.2

Phase sequence: K 123 N (1 1 1 ) I Δε: -7.4

Δη: 0.1649

Clp: 134.4 °C

γι : 933 mPa s

(all values extrapolated from 5% solution)

Example 5: 1 ,2,8-trifluoro-7-pentoxy-3-propoxy-dibenzofuran

This com ound is prepared from the common intermediate with Example 2.

Potassium phosphate (2.1 g, 9.4 mmol) is added to a stirred solution of 2- (2,5-difluoro-4-pentoxy-phenyl)-3,4-difluoro-5-propoxy-phenol (3.0 g, 7.8 mmol) in 1 ,3-dimethyl-3,4,5,6-tetrahydro-2(1 H)-pyrimidinone (35 ml_). The reaction mixture is stirred overnight at 1 10 °C, before it is treated with sat. NaCI solution and methyl tert-butyl ether. The aqueous phase is separated and extracted two times with methyl tert-butyl ether. The combined organic phase is washed with sat. NaCI solution, dried over Na₂SO₄, filtered and concentrated under reduced pressure. The residue is purified by

chromatography (heptane / chlorobutane) and recrystallization from ethanol to afford 1 ,2,8-trifluoro-7-pentoxy-3-propoxy-dibenzofuran as colourless crystals. ¹H NMR: δ 7.64 (dd, J = 10.5, 2.8 Hz, 1 H), 7.50 (d, J = 6.8 Hz, 1 H), 7.35 (d, J = 5.8 Hz, 1 H), 4.15 (td, J = 6.4, 3.8 Hz, 4H), 1 .79 (dq, J = 10.0, 6.8 Hz, 4H), 1 .51 - 1 .29 (m, 4H), 1 .02 (t, J = 7.3 Hz, 3H), 0.91 (t, J = 7.0 Hz, 3H). ¹⁹F NMR: δ -138.55 (dd, J = 10.3, 7.0 Hz), -144.62 - -144.76 (m), -166.41 (dd, J = 21 .1 , 5.9 Hz). EI-MS: 366.0. m.p. 147 °C.

Phase sequence: K 147 I.

Example 6:

In analogy to Example 5, the following compound is prepared.

¹H NMR: 7.30 (d, J = 5.7 Hz, 1 H), 6.91 (dd, J = 5.6, 1 .7 Hz, 1 H), 4.06 (t, J = 6.5 Hz, 2H), 2.75 (td, J = 7.7, 1 .4 Hz, 2H), 1 .91 (dtd, J = 13.9, 7.4, 6.4 Hz, 2H), 1 .74 - 1 .61 (m, 2H), 1 .36 (h, J = 3.5 Hz, 4H), 1 .09 (t, J = 7.4 Hz, 3H), 0.96 - 0.85 (m, 3H). EI-MS: 350.2

Phase sequence: K 88 I

Δε: -4.8

Δη: 0.1291

Clp: -49.6 °C

γι : 103 mPa s

(all values extrapolated from 5% solution)

Example 7

In analo to Example 5, the following compound is prepared.

¹H NMR (Chloroform-c/) δ 7.61 (d, J = 10.3 Hz, 1 H), 7.1 1 (d, J = 6.7 Hz, 1 H), 6.91 (dd, J = 5.6, 1 .7 Hz, 1 H), 4.09 (t, J = 6.6 Hz, 2H), 3.88 (d, J = 6.4 Hz, 2H), 2.02 - 1 .76 (m, 7H), 1 .63 - 1 .47 (m, 5H), 1 .32 - 0.84 (m, 13H). ¹⁹F NMR: δ -138.83 (dd, J = 10.3, 6.8 Hz), -144.10 (dd, J = 20.1 , 2.0 Hz), - 165.98 (dd, J = 20.0, 5.3 Hz). EI-MS: 434.204.

Phase sequence: K 142 I

The solubility of Comparative Examples 1 and 2 and Example 1 are measured following the procedure described above. The results are shown in Table 1 . Tablel .

As can be seen, the compound of Example 1 has an excellent solubility in cyclohexane as opposed to compounds of the state of the art, the solubility of which is very low.

The compounds according to the invention are distinguished by a high dielectric anisotropy and high solubility, which makes them very suitable for applications in liquid crystalline media for VA, IPS and FFS displays.

Claims

Patent Claims A Compound of formula I

in which

W denotes O or S, L¹ denotes R¹ or X¹,

L² denotes R² or X², each, independently of one another, denote H, an alkyl or alkoxy radical having 1 to 15 C atoms, where, in addition, one or more CH₂ groups in these radicals may each be replaced, independentl of one another, by -C≡C- , -CH=CH-

, -CF₂O-, -OCF₂-, -O-, -S-, -CO-O- or -O-CO- in such a way that O- or S-atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by CN or halogen,

X² independently of one another, denote halogenated alkyl, halogenated alkoxy, halogenated alkenyl or halogenated alkenyoxy, each having up to 5 C atoms, F, CI, CN, SCN, SF₅, A² each, independently of one another, denote a radical selected from the following groups: a) the group consisting of trans-1 ,4-cyclohexylene, 1 ,4-cyclohexenylene, and decaline-2,6-diyl, in which one or more non-adjacent CH2 groups may be replaced by - O- and/or -S- and in which one or more H atoms may be replaced by F, b) the group consisting of 1 ,4-phenylene and 2,6- naphthylene, in which one or two CH groups may be replaced by N and in which, in addition, one or more H atoms may be replaced by L, c) the group consisting of cyclopentane-1 ,3-diyl, cyclopent-2-ene-1 ,3-diyl, 1 ,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl, cyclobutane-1 ,3-diyl,

thiophene-2,5-diyl, selenophene-2,5-diyl, and

1 ,2,3,4-tetrahydronanaphthaline-2,6-diyl, each of which may be mono- or polysubstituted by L, d) the group consisting of bicyclo[1 .1 .1 ]pentane-1 ,3- diyl, bicyclo[2.2.2]octane-1 ,4-diyl, and spiro[3.3]heptane- 2,6-diyl, in which one or more H atoms may be replaced by F

L each, identically or differently, denote halogen, cyano, alkyl, alkoxy, alkylcarbonyl or alkoxycarbonyl group with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or CI, independently of one another, denote a single bond, -CF2O-, -OCF2-, -CH2CH2-, -CF2CF2-, -C(O)O-, -OC(O)- -CH2O-, -OCH2-, -CF=CH-, -CH=CF-, -CF=CF-,

-CH=CH- or -C≡C-.

Y¹, Y²,

Y³ and Y⁴ independently of one another, denote H, F, CI, CN, CF₃ or OCF₃ m and n are, independently of one another, 0, 1 or 2, while m + n is 0, 1 or 2, with the proviso that at least one of Y¹, Y², Y³ and Y⁴ is different from F and that at least one of Y¹, Y², Y³ and Y⁴ is different from H.

2. The Compound according to claim 1 , where the compound is

selected from the group of compounds of the sub-formula IA

IB

in which the occurring groups and parameters have the meanings indicated in claim 1 .

The Compound according to claim 1 or 2, where each, independently of one another, denote straight cha alkyl, alkenyl or alkoxy having up to 7 C atoms, or cydopropyl, cydobutyl, cydopentyl or cyclopen-1 -enyl, denotes F, CF₃ or OCF₃, denotes a radical selected from the following groups:

Z¹ denotes -CH₂O-, -CH₂CH₂- or a single bond

Y¹, Y²,

Y³ and Y⁴ denote H or F,

with the proviso that at least one of Y¹, Y², Y³ and Y⁴ is H, and m is 0 or 1 .

The compound according to one or more of claims 1 to 3, where m is 1 and Z¹ denotes a single bond or -CH₂O-.

The compound according to one or more of claims 1 to 3, where m is 0.

The Compound according to one or more of claims 1 to 5, where Y¹ denotes H and Y², Y³ and Y⁴ all denote F.

The Compound according to one or more of claims 1 to 5, where Y² denotes H and Y¹, Y³ and Y⁴ all denote F.

8. The Compound according to one or more of claims 1 to 5, where Y³ denotes H and Y¹, Y² and Y⁴ all denote F

9. The Compound according to one or more of claims 1 to 5, where Y denotes H and Y¹, Y² and Y³ all denote F.

The compound according to one or more of claims 1 to 5, where Y¹ and Y⁴ both denote F and Y² and Y³ both denote H.

1 1 . A compound of formula II

in which the occurring groups and parameters have the meanings indicated above for formula I, and

R" denotes alkyl having 1 to 5 C atoms, or phenyl in which one or two =CH- groups may be replaced by =N- and one or more H atoms may be replaced by halogen or alkyl having 1 to 10 C atoms.

12. A Process for the preparation of compounds of formula I according to one or more of claims 1 to 10, which comprises intramolecular reaction of a compound of formula II of claim 1 1 catalysed by a palladium catalyst in an aprotic organic solvent.

13. Use of a compound according to one or more of claims 1 to 10 in liquid-crystalline media.

14. Liquid-crystalline medium, characterised in that it comprises one or more compounds of formula I according to one or more of claims 1 to 10.

15. Electro-optical display element containing a liquid-crystalline medium according to claim 14.