CN110325522B

CN110325522B - Liquid crystal compounds

Info

Publication number: CN110325522B
Application number: CN201880009876.9A
Authority: CN
Inventors: C·布罗克; A·格茨
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2017-02-03
Filing date: 2018-01-31
Publication date: 2022-07-22
Anticipated expiration: 2038-01-31
Also published as: WO2018141759A1; TW201840828A; CN110325522A; DE102018000075A1; TWI761441B

Abstract

The present invention relates to compounds of formula (I),

wherein R is¹、L¹、L²And X has the meaning indicated in claim 1, to processes for their preparation, to liquid-crystalline media comprising at least one compound of the formula I, and to electro-optical displays comprising liquid-crystalline media of this type.

Description

Liquid crystal compounds

The present invention relates to compounds of formula I as defined below, to a process for their preparation, to a liquid-crystalline medium comprising at least one compound of formula I, and to their use as component(s) in a liquid-crystalline medium. Furthermore, the invention relates to liquid-crystal and electro-optical display elements comprising the liquid-crystalline medium according to the invention. The compounds according to the invention have as structural element a characteristically substituted 2- (4-phenylcyclohex-3-enyl) -1, 3-dioxanyl radical.

In the past years, the application fields of liquid crystal compounds have been greatly expanded to various types of display devices, electro-optical devices, electronic components, sensors, and the like. For this reason, many different structures have been proposed. Particularly in the field of nematic liquid crystals. Nematic liquid crystal mixtures have hitherto found the most widespread use in flat panel display devices. They are used in particular for passive TN or STN matrix displays or systems with TFT active matrix.

The liquid-crystalline compounds according to the invention can be used as component(s) of a liquid-crystalline medium, in particular for displays based on the principle of the twist-box, guest-host effect, aligned phase deformation DAP or ECB (electrically controlled birefringence) effect, IPS (in-plane switching) effect or dynamic scattering effect.

The use of tricyclic polar dioxane compounds as liquid crystalline materials is not known to those skilled in the art. Various compounds containing dioxane rings have been described as liquid crystalline or mesogenic materials and their preparation is described, for example, in the specification of CN 105038816 a. The compounds proposed therein do not contain a cyclohexene ring. The compound comprises, for example-OCF₃Or fluorine as polar end group.

It is an object of the present invention to find novel stabilizing compounds which are suitable as component(s) of liquid-crystalline media. In particular, the compounds should have both a relatively low viscosity and a high dielectric anisotropy. For many current mixture concepts in the field of liquid crystals, it is advantageous to use compounds having a combination of positive dielectric anisotropy Δ ∈ with medium to high optical anisotropy.

In view of the very broad field of application of such compounds having a high Δ ∈ it is desirable to have further compounds preferably having a high clearing point and a low viscosity, which have properties precisely adapted to the respective application.

It was therefore an object of the present invention to find new stabilizing compounds which are suitable as component(s) of liquid-crystalline media, in particular for TN, STN, IPS, FFS and TN-TFT displays, for example.

Furthermore, the compounds according to the invention are thermally and photochemically stable under the conditions prevailing in the field of application. As mesogens, they should favor a broad nematic phase in mixtures with liquid-crystalline co-components and be readily miscible with nematic base mixtures, especially at low temperatures. Substances with low melting points and low enthalpies of fusion are likewise preferred, since these parameters are also indicative of the desired properties mentioned above, such as high solubility, broad liquid-crystalline phases and a low tendency to spontaneously crystallize in the mixture at low temperatures. In particular, solubility at low temperatures is important for safe handling and transport of displays in vehicles and airplanes, as well as outdoors, avoiding any crystallization.

Surprisingly, it has been found that the compounds according to the invention are very suitable as components of liquid-crystalline media. Liquid-crystalline media for displays which require particularly high dielectric anisotropy, in particular for IPS or FFS displays, but also for TN or STN displays, are obtained by means of the compounds. The compounds according to the invention are sufficiently stable and colorless. In particular, they are distinguished by a high dielectric anisotropy Δ ∈ and therefore require a lower layer thickness and thus, when used in optical switching elementsThis requires a lower threshold voltage. They have good solubility for compounds with comparable properties. Furthermore, the compounds according to the invention have a relatively very high clearing point and at the same time a low rotational viscosity value. The compound has a relatively low melting point. With the aid of the compounds according to the invention, it is surprisingly possible to prepare compounds having a high elastic constant (K)¹¹/K²²/K³³) Without adversely affecting other use parameters. This results in a medium with a short response time and a high contrast.

The provision of the compounds according to the invention considerably broadens the scope of the liquid-crystalline substances which are suitable for the preparation of liquid-crystalline mixtures from the point of view of various applications.

The compounds according to the invention have a wide range of applications. Depending on the choice of substituents, these compounds can serve as base materials, from which the liquid-crystalline medium predominantly consists. However, it is also possible to add liquid-crystalline base materials composed of other kinds of compounds to the compounds according to the invention, in order, for example, to influence the dielectric and/or optical anisotropy of this type of dielectric and/or to optimize its threshold voltage and/or its viscosity.

The invention therefore relates to compounds of the formula I,

wherein

X represents CF₃、OCF₃、F、Cl、OCHF₂、CHF₂、SCN、CN、-C≡C-CF₃or-CH-CF₃，

R¹Denotes alkyl having 1 to 15C atoms, wherein one or more CH in these radicals₂The radicals may each, independently of one another, be-C.ident.C-, -CF₂O-、-OCF₂-、-CH＝CH-、

-O-, -S-, -CO-O-or-O-CO-with OS atoms are not directly linked to one another and in which one or more H atoms may be replaced by halogen, or H,

preferably represents a halogenated or unsubstituted alkyl radical having 1 to 15C atoms, in which one or more CH groups are present₂The radicals may each, independently of one another, be replaced by-C.ident.C-or-CH ═ CH-, and

L¹and L²Independently of one another, H or F, preferably H.

The invention also relates to the use of the compounds of formula I in liquid-crystalline media.

The invention likewise relates to liquid-crystalline media having at least two liquid-crystalline components which comprise at least one compound of the formula I.

The compounds of formula I have a wide range of applications. Depending on the choice of substituents, these compounds can serve as base materials, from which the liquid-crystalline medium consists predominantly; however, it is also possible to add the compounds of the formula I to liquid-crystalline base materials composed of other classes of compounds, in order, for example, to influence the dielectric and/or optical anisotropy of this type of dielectric and/or to optimize its threshold voltage and/or its viscosity.

In the pure state, the compounds of the formula I are colorless and form liquid-crystalline mesophases as such or in the form of mixtures in the temperature range which is advantageous for optoelectronic applications. The compounds according to the invention enable a wide nematic phase range. In liquid-crystalline mixtures, the substances according to the invention significantly increase the optical anisotropy and/or lead to an improvement in the low-temperature storage stability compared to comparable mixtures having a high dielectric anisotropy. At the same time, these compounds are characterized by good UV stability.

Formula I and a radical R in the subformula¹Preferably an alkyl or alkenyl group having up to 8 carbon atoms. R is¹Particularly preferably a straight-chain alkyl group having 1 to 7C atoms or an unbranched alkenyl group having 2 to 8C atoms, in particular an unbranched alkyl group having 2 to 7C atoms.

The group X in formula I preferably represents CF₃、OCF₃、F、-SCN、-C≡C-CF₃or-CH-CF₃Particularly preferably CF₃、OCF₃Or F, very particularly preferably CF₃Or OCF₃. The radical-CH-CF₃Preferably in the trans configuration.

With branched or substituted flanking groups (wing groups) R¹The compounds of formula I may occasionally be of importance because of better solubility in conventional liquid crystal base materials. Radical R¹Preferably linear.

Preferably wherein L¹A compound of formula I representing H, in particular wherein L¹And L²A compound of formula I representing H.

Radical R¹Particularly preferably selected from the following moieties:

-CH₃

-C₂H₅

-C₃H₇

-C₄H₉

-C₅H₁₁

-C₆H₁₃

-CH＝CH₂

-CH＝CH₂-CH₃

-CH₂-CH₂-CH＝CH₂

-CH₂-CH₂-CH＝CH-CH₃

wherein the alkyl chain is preferably unbranched (n-alkyl).

Particularly preferred compounds of formula I are compounds of formulae I-1 to I-6:

wherein R is¹Independently of the other have the meanings given above. Of the compounds of the formulae I-1 to I-6, preference is given to compounds of the formulae I-1, I-2, I-4 and I-5, in particular of the formulae I-1 and I-2.

Very particularly preferred compounds are given below:

the compounds of the formula I are prepared by methods known per se, such as are described in the literature (for example in 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 suitable for the reaction in question. Variants known per se and not mentioned here in detail can also be used here.

Compounds of formula I can be advantageously prepared as shown in the following illustrative syntheses and examples (schemes 1 through 3):

scheme 1. general synthetic schemes for the preparation of compounds of formula I. Bn represents a benzyl group. X represents a group X as in formula I. R is¹Represents a group R as in formula I¹。

Two polar end groups-CH ═ CH-CF₃and-C.ident.C-CF₃Can be prepared as follows:

scheme 2. end group X ═ -CH ═ CH-CF₃and-C.ident.C-CF₃Synthesizing; ar represents a substituted phenyl group of the compound of formula I. In the first step, a molecular sieve is preferably added for absorbing water.

Reversing the reaction sequence from scheme 1 alternatively results in synthesis scheme 3.

Scheme 3. alternative general synthetic schemes for the preparation of compounds of formula I. R¹And X is defined according to formula I.

The corresponding starting materials are generally readily preparable by synthetic methods known from the literature or are commercially available to the person skilled in the art.

Instead of the grignard compounds shown in schemes 1 and 3, it is also possible to use aryllithium compounds which are similarly obtainable by halogen-metal exchange with alkyllithium compounds at low temperatures (see for example US 4,940,822).

The invention therefore also relates to a process for preparing a compound of the formula I, which comprises the process steps of, an aryl metal compound of the formula II

X, L therein¹And L²As defined for formula I, and

m represents Li, MgBr or MgCl,

with compounds of the formula III

Wherein PG represents a protecting group, preferably a benzyl group,

and in a further reaction step comprises the removal of the protecting group PG (replaced by H) and the resulting CH₂Oxidation of the OH group to give the aldehyde CH ═ O,

with 2-substituted 1, 3-diols of the formula IV

To give a compound of the formula I

Wherein the radicals are as defined above.

The reaction methods and reagents used are generally known from the literature. Further reaction conditions are revealed by the working examples.

Further preferred process variants not mentioned above are disclosed by the examples or claims.

The process and the subsequent work-up of the reaction mixture can be carried out essentially as a batch reaction or as a continuous reaction process. Continuous reaction processes include, for example, reactions in continuous stirred tank reactors, stirred reactor cascades, loop or cross-flow reactors, flow tubes or microreactors. If desired, the reaction mixture is optionally worked up by solid phase filtration, chromatography, separation between immiscible phases (e.g. extraction), adsorption onto a solid support, removal of the solvent and/or azeotropic mixture by distillation, selective distillation, sublimation, crystallization, co-crystallization or by nanofiltration on a membrane.

In the present invention, a 2, 5-disubstituted dioxane ring of the formula

Preferably, the dioxane rings are represented in the 2, 5-trans configuration, i.e. the substituents are in a preferred chair conformation, preferably all in an equatorial position.

The invention also relates to liquid-crystalline media comprising one or more compounds of the formula I according to the invention. The liquid-crystalline medium comprises at least two components. They are preferably obtained by mixing the components with one another. The process according to the invention for preparing a liquid-crystalline medium is therefore characterized in that at least one compound of the formula I is mixed with at least one further mesogenic compound and, optionally, additives are added.

The combination of clearing point, low temperature viscosity, thermal/UV stability, dielectric anisotropy, response time and contrast achievable is far superior to prior art materials.

In addition to one or more compounds according to the invention, the liquid-crystalline media according to the invention preferably comprise from 2 to 40, particularly preferably from 4 to 30, components as further constituents. In particular, these media comprise from 7 to 25 components in addition to one or more compounds according to the invention. These further components are preferably selected from nematic or nematic (unidirectional or isotropic) substances, in particular from the following classes: azoxybenzene, benzylideneaniline, biphenyl, terphenyl, phenyl benzoate or cyclohexyl benzoate, phenyl or cyclohexyl cyclohexanecarboxylate, phenyl or cyclohexyl cyclohexylbenzoate, phenyl or cyclohexyl cyclohexylcyclohexanecarboxylate, phenyl or cyclohexyl cyclohexylphenyl benzoate, cyclohexane carboxylic acid or cyclohexylcyclohexanecarboxylate, phenyl cyclohexane, cyclohexylbiphenyl, phenyl cyclohexylcyclohexane, 1, 4-dicyclohexylbenzene, 4,4' -dicyclohexylbiphenyl, phenyl or cyclohexylpyrimidine, phenyl or cyclohexylpyridine, phenyl or cyclohexyldioxane, phenyl-or cyclohexyl-1, 3-dithiane, 1, 2-diphenylethane, 1, 2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenylcyclohexyl) ethane, 1-cyclohexyl-2-diphenylethane, 1-phenyl-2-cyclohexylphenylethane, optionally halogenated stilbene, benzylphenyl ether, tolane and substituted cinnamic acids. The 1, 4-phenylene groups in these compounds may also be fluorinated.

The most important compounds suitable as further components of the medium according to the invention can be characterized by the formulae 1,2, 3, 4 and 5:

R'-L-E-R" 1

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

R'-L-CF₂O-E-R" 3

R'-L-CH2CH2-E-R" 4

R'-L-C≡C-E-R" 5

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

One of the radicals L and E is preferably Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. The medium according to the invention preferably comprises: one or more components selected from the group consisting of compounds of formulas 1,2, 3, 4, and 5, wherein L and E are selected from the group consisting of Cyc, Phe, and Pyr; and one or more components selected from the group consisting of compounds of formulae 1,2, 3, 4 and 5, wherein one of the groups L and E is selected from Cyc, Phe, Py and Pyr and the other is selected from-Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe-and-G-Cyc-; and optionally one or more components selected from the group consisting of compounds of formulae 1,2, 3, 4 and 5, wherein the groups L and E are selected from the group consisting of-Phe-Cyc-, -Cyc-Cyc-, -G-Phe-and-G-Cyc-.

R 'and/or R' each, independently of one another, denote alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8C atoms, -F, -Cl, -CN, -NCS or- (O)_iCH_3-kF_kWherein i is 0 or 1 and k is 1,2 or 3.

In a smaller subgroup of the compounds of formulae 1,2, 3, 4 and 5, R' and R "each, independently of the others, represent alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8C atoms. The smaller subgroups are referred to below as group a and the compounds are represented by sub-formulae 1a, 2a, 3a, 4a and 5 a. In most of these compounds, R 'and R' are different from each other, one of these groups usually being an alkyl, alkenyl, alkoxy or alkoxyalkyl group.

In another smaller sub-group of compounds of formulae 1,2, 3, 4 and 5, designated as group B, R' represents-F, -Cl, -NCS or- (O) iCH3-kFk, wherein i is 0 or 1 and k is 1,2 or 3. The compounds in which R' has this meaning are represented by the sub-formulae 1b, 2b, 3b, 4b and 5 b. Particularly preferred are compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, wherein R "has the meaning-F, -Cl, -NCS, -CF3, -OCHF2 or-OCF 3.

In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, R' has the meaning indicated in the case of the compounds of the sub-formulae 1a to 5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller subgroup of the compounds of formulae 1,2, 3, 4 and 5, R "represents — CN. This subgroup is referred to below as group C and the compounds of this subgroup are described by sub-formulae 1C, 2C, 3C, 4C and 5C, respectively. In the compounds of the sub-formulae 1c, 2c, 3c, 4c and 5c, R' has the meaning indicated in the case of the compounds of the sub-formulae 1a to 5a and is preferably alkyl, alkoxy or alkenyl.

In addition to A, B and the preferred compounds of group C, other compounds of formulas 1,2, 3, 4, and 5 with other variations of the substituents set forth are also conventional. All these substances can be obtained by methods known in the literature or analogously thereto.

In addition to the compounds of the formula I according to the invention, the media according to the invention preferably comprise one or more compounds selected from group A, B and/or C. In the medium according to the invention, the proportions by weight of the compounds from these groups are preferably:

group A: 0 to 90%, preferably 20 to 90%, particularly preferably 30 to 90%;

group B: 0 to 80%, preferably 10 to 80%, particularly preferably 10 to 65%;

group C: 0 to 80%, preferably 0 to 80%, particularly preferably 0 to 50%;

the sum of the proportions by weight of A, B and/or group C compounds present in the respective media according to the invention is preferably from 5 to 90%, particularly preferably from 10 to 90%.

The media according to the invention preferably comprise from 1 to 40%, particularly preferably from 3 to 30%, of the compounds according to the invention.

The liquid-crystal mixtures according to the invention are prepared in a manner conventional per se. In general, the desired amount of the components used in smaller amounts is dissolved in the components making up the main constituent, preferably at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again after thorough mixing, for example by distillation. The mixture may also be prepared in other conventional ways, for example by using a premix, for example an homo-mixture, or using a so-called "multi-vial" system.

The dielectric may also contain further additives known to the person skilled in the art and described in the literature. For example, 0 to 15%, preferably 0 to 10%, of pleochroic dyes, chiral dopants, stabilizers or nanoparticles may be added. Each compound added is used at a concentration of 0.01 to 6%, preferably 0.1 to 3%. However, concentration data for the other components of the liquid crystal mixture (i.e. the liquid crystal or mesogenic compounds) are given here without taking into account the concentrations of these additives.

The liquid-crystal mixtures according to the invention enable a significant expansion of the usable parameter range.

The invention also relates to electro-optical displays comprising a medium of this type (in particular TFT displays with two plane-parallel substrates which together with a frame form a cell, an integrated non-linear element for switching individual pixels on the substrate, and a nematic liquid-crystal mixture with positive dielectric anisotropy and high resistivity located in the cell), and to the use of these media for electro-optical purposes.

The expression "alkyl" encompasses the unbranched and branched alkyl radicals having from 1 to 15 carbon atoms, in particular the unbranched radicals methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl and n-heptyl. Groups having 2 to 5 carbon atoms are generally preferred.

The expression "alkenyl" includes unbranched and branched alkenyl groups having up to 15 carbon atoms, in particular unbranched radicals. Particularly preferred alkenyl is C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, especially C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl. Examples of preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are generally preferred.

The expression "haloalkyl" preferably includes mono-or polyfluoro-and/or mono-or polychlorinated groups. Including perhalogenated groups. Fluoroalkyl groups, in particular CF, are particularly preferred₃、CH₂CF₃、CH₂CHF₂、CHF₂、CH₂F、CHFCF₃And CF₂CHFCF₃. The expression "haloalkenyl" and related expressions are interpreted accordingly.

The total amount of the compounds of the formula I in the mixtures according to the invention is not critical. Thus, the mixture may comprise one or more additional components for the purpose of optimizing various properties.

The construction of the matrix display of the invention, consisting of polarisers, electrode substrates and surface-treated electrodes, corresponds to the conventional design of such displays. The term "conventional design" is here to be understood in a broad sense and also encompasses all derivatives and variants of matrix displays, in particular also matrix display elements based on poly-Si TFTs.

However, a significant difference between the display according to the invention and the conventional displays based on twisted nematic cells to date lies in the choice of the liquid crystal parameters of the liquid crystal layer.

The following examples illustrate but do not intend to limit the present invention. A person skilled in the art will be able to gather from the embodiments the working details not given in the general description, to generalize them according to the general expert knowledge and to apply them to specific problems.

In this context, percentage data represent weight percentages. All temperatures are expressed in degrees celsius. Further, C ═ crystalline, N ═ nematic, Sm ═ smectic (more specifically, SmA, SmB, etc.), Tg ═ glass transition temperature, and I ═ isotropic. The data between these symbols represents the transition temperature. Δ n represents optical anisotropy (589nm, 20 ℃ C.), Δ ε represents dielectric anisotropy (1kHz, 20 ℃ C.), and γ₁The rotational viscosity (20 ℃ C.; unit mPas) was measured.

The physical, physicochemical and electro-optical parameters are determined by generally known methods, in particular as described in the manual "Merck Liquid Crystals-

-Physical Properties of Liquid Crystals-Description of the Measurement Methods ", 1998, Merck KGaA, Darmstadt.

The dielectric anisotropy. DELTA.. di-elect cons.of each substance was measured at 20 ℃ and 1 kHz. For this purpose, 5 to 10% by weight of the substance to be investigated dissolved in the dielectrically positive mixture ZLI-4792(Merck KGaA) are measured and the measured values are extrapolated to a concentration of 100%. Optical anisotropy Deltan measured at 20 deg.C and 589.3nm wavelength, rotary viscosity gamma₁The measurement was carried out at 20 ℃ and both were also measured by linear extrapolation.

In this application, the plural forms of terms refer to the singular and plural forms, and vice versa, unless explicitly stated otherwise. Further combinations of embodiments and variants of the invention according to the description also result from the following claims or combinations of a plurality of these claims.

The following abbreviations are used:

DCM dichloromethane

DMSO dimethyl sulfoxide

EA ethyl acetate

MTB Ether methyl Tertiary butyl Ether

THF tetrahydrofuran

Example 1: 5-propyl-2- [4- (4-trifluoromethylphenyl) cyclohex-3-enyl ] -1, 3-dioxane

Step 1

2.2g (16mmol) of magnesium turnings were first added to a small amount of THF, and 20.3g (90mmol) of 4-bromotrifluorotoluene 1 were dissolved in 50ml of THF and added dropwise at such a rate that the reaction mixture was boiled. The mixture was then heated at reflux for 1 hour. The heat source was temporarily removed and 20.0g (90mmol) of 4-benzyloxymethyl-cyclohexanone 2 was added to the batch, followed by heating under reflux for a further 2 hours and stirring at room temperature for 18 hours. The batch is poured into ice water and adjusted to pH 2 with 2M hydrochloric acid. The aqueous phase was separated and extracted with MTB ether. The combined organic phases were washed with sodium chloride solution, dried over sodium sulfate, filtered and evaporated to give 4-benzyloxymethyl-1- (4-bromophenyl) cyclohexanol 3 as a red-brown oil, which was used for the next reaction step without further purification.

Step 2:

12g of Pd/C catalyst (112 mmol; 5% on active carbon) are added to a solution of 34.1g (78mmol) of crude product 3 in 340ml of THF. The protecting group was cleaved using 2.34l hydrogen. The catalyst was then filtered off. The hydrogenated solution was evaporated to dryness to give 4-hydroxymethyl-1- (4-trifluoromethylphenyl) cyclohexanol as a brown oil.

And step 3:

first, 7.27ml (85mmol) of oxalyl chloride was added to 100ml of DCM and a solution of 12ml (170mmol) of DMSO (dry) in 80ml of DCM was added dropwise at-60 ℃. A solution of 10.2g (13mmol) of 4-hydroxymethyl-1- (4-trifluoromethylphenyl) cyclohexanol 4 in 310ml of DCM is then added dropwise. After stirring for a period of 15 minutes, 53ml of triethylamine were added. After stirring for 5 minutes, the cooling bath was removed. The mixture was then hydrolyzed with water at room temperature and diluted with DCM. The aqueous phase was separated and extracted with DCM. The combined organic phases are washed with water and sodium chloride solution, dried over sodium sulfate, filtered and evaporated to dryness. The crude product was then purified by silica gel chromatography (DCM/EA 8:2) to give 4-hydroxy-4- (4-trifluoromethylphenyl) cyclohexanecarboxaldehyde 5 as a yellow oil.

And 4, step 4:

16.8g (54mmol) of 4-hydroxy-4- (4-trifluoromethylphenyl) cyclohexanecarboxaldehyde 5 are initially introduced into 284ml of toluene. 7.61g (64mmol) of 2-n-propylpropane-1, 3-diol and 1.39g (8mmol) of toluene-4-sulfonic acid monohydrate were added and the mixture was heated under reflux on a water separator for 1.5 hours. When the reaction was complete, the reaction mixture was directly chromatographed on silica gel. Two crystallizations from isopropyl alcohol/acetone and methylcyclohexane/heptane yielded 5-propyl-2- [4- (4-trifluoromethylphenyl) cyclohex-3-enyl ] -1, 3-dioxane 6 as white, lustrous crystals.

C 120SmB 164I

Δε＝22

Δn＝0.107

γ₁＝395mPa·s

The following are prepared in a similar or equivalent manner:

C 89SmA 94N 117I

Δε＝13.4

Δn＝0.104

γ₁＝299mPa·s

C 72SmB 160SmA 166I

Δε＝17

Δn＝0.106

γ₁＝211mPa·s

C 111I

Δε＝26

Δn＝0.101

γ₁＝380 mPa·s

C 55 SmA 132 I

Δε＝20

Δn＝0.101

γ₁＝248 mPa·s

C 70 SmA 86 N 89 I

Δε＝18

Δn＝0.090

γ₁＝247 mPa·s

C 55 SmA(43)N(51)I

Δε＝22.5

Δn＝0.073

γ₁＝168 mPa·s

C 67 SmA 88 I

Δε＝24.5

Δn＝0.099

γ₁＝258 mPa·s

C 95 I

Δε＝32

Δn＝0.095

γ₁＝275 mPa·s

Claims

1. a compound of the formula I,

wherein

R¹Represents an alkyl radical having 1 to 15C atoms, wherein one or more CH groups of these radicals₂The radicals may each, independently of one another, be replaced by-C.ident.C-, -CH-),

-O-、-S-、-CO-or-O-CO-is replaced in such a way that the O and S atoms are not directly linked to each other, and wherein one or more H atoms may be replaced by halogen,

L¹and L²Independently of one another, H or F.

2. A compound according to claim 1,

L¹represents H.

3. A compound according to claim 1 or 2, characterized in that,

R¹represents an alkyl or alkenyl group having up to 8 carbon atoms.

4. A compound according to claim 1 or 2, characterized in that,

x represents OCF₃、CF₃Or F.

5. Compound according to claim 1 or 2, characterized in that L¹And L²Represents H.

6. Compound according to claim 1 or 2, characterized in that X represents CF₃。

7. Compound according to claim 1 or 2, characterized in that X represents OCF₃。

8. A compound according to claim 1 or 2 selected from the following formulae:

wherein R is¹Have the meaning indicated in claim 1 or 3.

9. Compound according to claim 1 or 2, characterized in that R¹Represents a straight-chain alkyl group having 1 to 7C atoms or an unbranched alkenyl group having 2 to 8C atoms.

10. A process for the preparation of a compound of formula I according to any one of claims 1 to 9, comprising the process steps wherein an aryl metal compound of formula II

X, L therein¹And L²As defined by formula I according to any one of claims 1 to 9, and

m represents Li, MgBr or MgCl,

with compounds of the formula III

Wherein PG represents a protecting group, which is a cyclic or cyclic alkyl group,

and in a further reaction step involving the removal of the protecting group PG and the resulting CH₂Oxidation of the OH group to give the aldehyde CH ═ O,

with 2-substituted 1, 3-diols of the formula IV

To give compounds of the formula I

Wherein the radical R¹、L¹、L²And X is as defined in claim 1.

11. Use of one or more compounds of formula I according to any one of claims 1 to 9 as a component in liquid-crystalline media.

12. Liquid-crystalline medium comprising at least two mesogenic compounds, characterized in that it comprises at least one compound of formula I according to any one of claims 1 to 9.

13. Use of a liquid-crystalline medium according to claim 12 for electro-optical purposes.

14. An electro-optical liquid-crystal display comprising a liquid-crystalline medium according to claim 12.