DE4344422A1 - 1=Phenyl-2=pyridyl- and pyrimidyl-acetylene(s) useful in liquid crystal media - Google Patents

Abstract

Pyri(mi)dine derivs. of formula (I) are new: R = alk(en)yl with up to 15C, opt. mono-substd. by CN, halogen or CF3, in which 1 or more -CH2- gps. may be replaced by -O-, -CO-, -CO-O-, -O-CO- or -O-CO-O-, without directly linked O atoms; ring A = (a) trans-1,4-cyclohexylene (cyc), in which 1 or more non-adjacent -CH2- gps. may be replaced by -O- and/or -S-; (b) 1,4-phenylene (PHe), in which 1 or 2 CH gps. may be replaced by N; or (c) 1,4-cyclohexylene, 1,4-bicyclo-(2.2.2)octylene, piperidin-1,4-diyl, naphtha-2,6-diyl, deca:hydrogen:naphtha-2,6-diyl or 1,2,3,4-tetra:hydro:naphtha-2,6-diyl; and the (a) and (b) gps. may be mono- or di-substd. by F; X = 1-10C alkyl or alkoxy or Q-Y; Q = -O-, -S- or a single bond; Y = H, F, Cl, Cn or a mono- or poly-halo-alk(en)yl gp. with up to 10C; Z = N or CH; L<1>,L<2> = H or F; m = 0, 1 or 2. Also claimed are liquid crystal (LC) media contg. cpd(s). (I), LCD elements contg. this medium and electrooptical display elements contg. the medium as dielectric.

Description

The present invention relates to pyri (mi) din derivatives of the formula I,

wherein
R is an unsubstituted or substituted by CN, halogen or CF₃ alkyl or alkenyl radical having up to 15 carbon atoms, wherein in these radicals also one or more CH₂ groups each independently by -O-, -CO-, -CO - O, -O-CO or -O-CO-O- can be replaced so that O atoms are not directly linked to each other,

• a) trans-1,4-cyclohexylene radical, wherein one or more non-adjacent CH₂ groups by -O- and / or -S- can be replaced
• b) 1,4-phenyl, wherein also one or two CH groups can be replaced by N,
• c) radical from the group 1,4-cyclohexylene, 1,4- Bicyclo [2.2.2] octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, Decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydro naphthalene-2,6-diyl,

where the radicals (a) and (b) can be substituted by one or two fluorine,
X is alkyl or alkoxy having 1-10 C atoms, or QY, where
Q is -O-, -S- or a single bond
Y is H, F, Cl, CN, mono- or polyhalogenated alkyl or alkenyl having up to 10 C atoms,
ZN or CH
L 1 and L 2 are each independently H or F, and
m 0, 1 or 2
mean.

The invention further relates to the use of these compounds as Components of liquid-crystalline media and liquid crystal and Electro-optical display elements, the inventive Liquid crystalline media included.

The compounds of the formula I can be used as components liquid-crystalline media are used, in particular for displays, based on the principle of the twisted cell, the guest-host effect, the Effect of deformation of erect phases or the effect of based on dynamic dispersion.

The compounds of formula I are partially from the very general formula in EP 0 306 505. There are only Pyri (mi) din derivatives of the formulas

R¹ = alkyl; R² = alkyl, alkoxy or chlorine
called.

The invention therefore an object of the invention, new stable to find liquid-crystalline or mesogenic compounds known as Components of liquid-crystalline media are suitable and in particular at the same time have a comparatively low viscosity and a relatively high dielectric anisotropy.

It has now been found that compounds of the formula I as Components of liquid-crystalline media are eminently suitable. In particular, they have comparatively low viscosities. With their help can be stable liquid crystalline media with a wide Mesophase range and favorable values for the optical and obtained dielectric anisotropy. These media also have a lot good low temperature behavior.

With the provision of compounds of formula I is also completely In general, the range of liquid-crystalline substances that are under various application-technical aspects for the production liquid-crystalline mixtures, significantly widened.

The compounds of the formula I preferably comprise the compounds of the Formulas I1-I18

If X is a halogenated alkyl, alkoxy or alkenyl radical, see this can be straight-chain or branched. Preferably, he is straight-chain and has 1, 2, 3, 4, 5, 6 or 7 carbon atoms; in the case of the alkenyl radical 2, 3, 4, 5, 6 or 7 carbon atoms.

X is preferably F, Cl, CN, OC _n F _{2n + 1} , C _n F _{2n + 1} , O (CH₂) _n -CF₃, O (CH₂) _n CF₂H, O (CH₂) _n -CHF₂, (CH₂) _n -CF₃, (CH₂) _n -CF₂H, (CH₂) _n -CHF₂, (CH₂) _n -CH = CF₂, (CH₂) _n -CF = CF₂, (CH₂) _n -CH = CFH, SC _n F _{2n + 1} , S (CH₂) _n CF₃, O (CH₂) _n -CCl₂, (CH₂) _n -CH = CCl₂ or (CF₂) _n -CF₂H, where n is 0 to 7. Particularly preferred are pyri (mi) din derivatives of the formula I, wherein X, F, Cl, CN, OCF₃, or OCH₂CF₃ means.

If R is an alkyl radical and / or an alkoxy radical, then this be straight-chain or branched. Preferably, it is straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and therefore preferably denotes 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.

Oxaalkyl is preferably straight-chain 2-oxapropyl (= methoxy methyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxa heptyl, 2-, 3-, 4-, 5-, 6- or 7-oxo-octyl, 2-, 3-, 4-, 5-, 6-, 7- or 8- Oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.  

If R is an alkyl radical in which a CH₂ group is replaced by -CH = CH- is replaced, it may be straight-chain or branched. Preferably it is straight-chain and has 2 to 10 carbon atoms. He means accordingly especially vinyl, prop-1, or prop-2-enyl, but-1 -, 2- or but-3-enyl, Pent-1-, 2-, 3- or pent-4-enyl, hex-1, 2-, 3-, 4- or hex-5-enyl, hept 1-, 2-, 3-, 4-, 5- or hept-6-enyl, oct-1, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, Non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, Dec-l, 2-, 3-, 4-, 5-, 6-, 7 - 8- or dec-9-enyl.

If R is an alkyl radical in which a CH₂ group by -O- and one replaced by -CO-, these are preferably adjacent. Thus These include an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. Preferably, these are straight-chain and have 2 to 6 C-atoms.

They therefore mean especially acetyloxy, propionyloxy, butyryloxy, Pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, Butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxy ethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4- Acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, Butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxy carbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (Methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxy carbonyl) ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl, 4- (Methoxycarbonyl) -butyl.

If R is an alkyl radical in which a CH₂ group by unsubstituted or substituted -CH = CH- and an adjacent CH₂- Group is replaced by CO or CO-O or O-CO, so this can straight-chain or branched. Preferably, it is straight-chain and has 4 up to 13 C-atoms. He therefore means especially acryloyloxymethyl, 2 Acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxy pentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl,  9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2- Methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxy-butyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxy heptyl, 8-methacryloyloxyoctyl, 9-methacryloyloxynonyl.

If R is a substituted by CN or CF₃ alkyl or Alkenyl means, this radical is preferably straight-chain and the Substitution by CN or CF₃ in the ω position.

If R represents an alkyl radical in which two or more CH₂ groups replaced by -O- and / or -CO-O-, it may be straight-chain or be branched. Preferably, it is branched and has 3 to 12 carbon atoms. It therefore means especially bis-carboxymethyl, 2,2-bis-carboxy ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxy pentyl, 6,6-bis-carboxyhexyl, 7,7-biscarboxy-heptyl, 8,8-bis-carboxy octyl, 9,9-bis-carboxy-nonyl, 10,1 0-bis-carboxydecyl, bis (methoxy carbonyl) methyl, 2,2-bis (methoxycarbonyl) methyl, 3,3-bis (methoxy carbonyl) -propyl, 4,4-bis (methoxycarbonyl) -butyl, 5,5-bis (methoxy carbonyl) -pentyl, 6,6-bis (methoxycarbonyl) -hexyl, 7,7-bis (methoxycar bonyl) - heptyl, 8,8-bis (methoxycarbonyl) octyl, bis (ethoxycarbonyl) - methyl, 2,2-bis (ethoxycarbony) ethyl, 3,3-bis (ethoxycarbonyl) propyl, 4,4-bis (ethoxycarbonyl) -butyl, 5,5-bis (ethoxycarbonyl) -hexyl.

If R is an alkyl or at least monosubstituted by halogen Alkenyl radical, this radical is preferably straight-chain and Halogen is preferably F or Cl. When multiple substitution is halogen preferably F. The resulting radicals also include perfluorinated Leftovers. For single substitution, the fluorine or chlorine substituent be in any position, but preferably in the ω position.

Compounds of formulas I with branched wing groups R can occasionally because of a better solubility in the usual liquid-crystalline base materials, in particular but as chiral dopants when they are optically active. smectic Compounds of this type are suitable as components for ferroelectric Materials.  

Branched groups of this type usually contain no more than one Chain branching. Preferred branched radicals R are isopropyl, 2- Butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, Isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methyl butoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methyl hexoxy, 1-methylheptoxy.

Compounds of the formula I which are suitable for polycondensations Have wing groups R, are suitable for the preparation of liquid crystalline Polycondensates.

Formula I includes both the racemates of these compounds and the optical antipodes and their mixtures.

Compounds of the formula I with SA phases are suitable, for example, for thermally addressed displays.

Among these compounds of formula I and the sub-formulas are those in which at least one of them contains Rests has one of the preferred meanings given.

In the compounds of formula I are those stereoisomers preferred in which the cyclohexane ring is trans-1,4-disubstituted.

The compounds of the formula I are prepared by methods known per se as described in the literature (eg in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme Verlag, Stuttgart), under reaction conditions conditions which are known and suitable for the reactions mentioned.

One can also of known per se, not mentioned here Make use of variants.  

If desired, the starting materials can also be formed in situ be such that they are not isolated from the reaction mixture, but immediately further to the compounds of formula I implements. The compounds of the invention can be z. B. following Produce reaction scheme easily.

Scheme 1

The preparation of some particularly preferred compounds is in Scheme 2.  

Scheme 2

The liquid-crystalline media according to the invention contain preferably in addition to one or more inventive Compounds as further constituents 2 to 40, in particular 4 to 30 Components. Most preferably, these media contain next one or more compounds 7 to 25 according to the invention Components. These other ingredients are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of Azoxybenzenes, Benzylidenanilines, biphenyls, terphenyls, phenyl or Cyclohexyl benzoates, cyclohexane-carboxylic acid phenyl or cyclohexyl ester, phenyl or cyclohexyl ester of cyclohexylbenzoic acid, phenyl or cyclohexyl ester of cyclohexylcyclohexanecarboxylic acid, cyclohexyl phenyl ester of benzoic acid, the cyclohexanecarboxylic acid or the Cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbi phenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclo  hexylcyclohexylcyclohexenes, 1,4-biscyclohexylbenzenes, 4,4'-bis cyclohexylbiphenyls, phenyl or cyclohexylpyrimidines, phenyl or Cyclohexylpyridines, phenyl or cyclohexyldioxanes, phenyl or cyclo hexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1 Phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenyl-cyclohexyl) -ethanes, 1-Cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexyl-phenylethanes, optionally halogenated stilbenes, benzylphenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these Compounds may also be fluorinated.

The most important as further constituents of inventive media in Questioning compounds can be represented by the formulas 1, 2, 3, 4 and 5 characterize:

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-C≡C-E-R '' 5

In formulas 1, 2, 3, 4 and 5, L and E denote the same or may be different, each one independently bivalent radical from the -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc- Cyc, -Pyr, -Dio, -G-Phe and -G-Cyc and their mirror images formed group, wherein Phe is unsubstituted or fluorinated substituted 1,4-phenylene, Cyc trans-1, 4-cyclohexylene or 1, 4- Cyclohexylene, Pyr pyrimidine-2-5-diyl or pyridine-2,5-diyl, Bio 1,3-dioxane 2,5-diyl and G 2- (trans-1,4-cyclohexyl) -ethyl, pyrimidine-2,5-diyl, pyridine 2,5-diyl or 1,3-dioxane-2,5-diyl.  

Preferably, one of L and E is Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. Preferably, the contain Media selected one or more components according to the invention from the compounds of formulas 1, 2, 3, 4 and 5, wherein L and E are selected from the group Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of Formulas 1, 2, 3, 4 and 5, wherein one of the radicals L and E is selected from the group Cyc, Phe and Pyr and the other radical is selected from the group -Phe-Phe, -Phe-Cyc, -Cyc-Cyc, -G-Phe and -G-Cyc-, and optionally one or more components selected from Compounds of Formulas 2, 2; 3, 4 and 5, wherein the radicals L and E are selected from the group -Phe-Cyc, -Cyc-Cyc, -G-Phe and -G- Cyc.

R 'and R "in a smaller subgroup of the compounds mean Formulas 1, 2, 3, 4 and 5 are each independently alkyl, alkenyl, Alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy of up to 8 Carbon atoms. The following is this smaller subgroup group A and the compounds are described with the sub-formulas 1a, 2a, 3a, 4a and 5a. For most of these compounds, R 'and R '' different from each other, wherein one of these radicals is usually alkyl, Alkenyl, alkoxy or alkoxyalkyl.

In a smaller subgroup of compounds of formulas 1, 2, 3, 4 and 5, other than group B, R '' is -F, -Cl, -NCS or - (O) _i CH ₃ - _{(k + 1)} F _k Cl₁, where i is 0 or 1 and k + 1 is 1, 2 or 3; the compounds in which R "has this meaning are designated by the subformulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the subformulae 1b, 2b, 3b, 4b and 5b in which R "has the meaning -F, -Cl, -NCS, -CF₃, -OCHF₂ or -OCF₃.

In the compounds of sub-formulas 1b, 2b, 3b, 4b and 5b R 'has the at the meaning of the compounds of sub-formulas 1a-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.  

In a further smaller subgroup of the compounds of the formulas 1, 2, 3, 4 and 5 are R "-CN; this subgroup is hereafter referred to as Group C and become the compounds of this subgroup according to sub-formulas 1c, 2c, 3c, 4c and 5c described. In the Compounds of sub-formulas 1c, 2c, 3c, 4c and 5c have R 'in the Compounds of the sub-formulas 1a-5a given meaning and is preferably alkyl, alkoxy or alkenyl.

In addition to the preferred compounds of groups A, B and C are also other compounds of formulas 1, 2, 3, 4 and 5 with other variants the proposed substituents in use. All these substances are available by literature methods or in analogy thereto.

The media according to the invention contain, in addition to the invention Compounds of the formula I preferably one or more Verbindun which are selected from group A and / or group B. and / or group C. The mass fractions of the compounds from these Groups on the media according to the invention are preferably

Group A:
0 to 90%, preferably 20 to 90%, in particular 30 to 90%
Group B:
0 to 80%, preferably 10 to 80%, especially 10 to 65%
Group C:
0 to 80%, preferably 5 to 80%, especially 5 to 50%

where the sum of the mass fractions in the respective Compounds of the invention contained in the groups A and / or B and / or C preferably 5 to 90% and especially 10 up to 90%.  

The media according to the invention preferably contain 1 to 40%, in particular preferably 5 to 30% of inventive Links. Further preferred are media containing more than 40%, in particular 45 to 90% of compounds according to the invention. The media preferably contain three, four or five inventive Links.

Preferred media may be in addition to the compounds of the invention of formula I consist only of group B compounds. Farther preferred are media which, in addition to the compounds of the formula I, Group B compounds and 0-20% Group A compounds and / or the group C included.

The preparation of the media according to the invention takes place in per se Wise. In general, the components are dissolved in each other, expedient at elevated temperature. By suitable additives can the liquid crystalline phases according to the invention are modified so that they are in all hitherto known types of Flüssigkristallan display elements can be used. Such additives are the Known in the art and described in detail in the literature (H. Kelker / R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes for the production colored guest host systems or substances for modifying the dielectric anisotropy, viscosity and / or orientation of the nematic phases are added.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, wherein the transformation into chemical formulas according to following Tables A and B takes place. All radicals C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl radicals with n or m C atoms. The coding according to Table B is self-evident. In Table A, only the acronym for the main body is given. In individual cases, followed by the acronym for the main body with a dash followed by a code for the substituents R¹, R², L¹, L² and L³:

Table A

Table B

The following examples are intended to illustrate the invention without going to limit. Above and below are percentages by weight percent. All temperatures are in degrees Celsius. Mp means Melting point, bp. = Clearing point. Furthermore, K = crystalline state, N = nematic phase S = smectic phase and 1 = isotropic phase. The Indications between these symbols represent the transition temperatures Δn means optical anisotropy (589 nm, 20 ° C) and viscosity (mm² / sec) was determined at 20 ° C.

"Usual workup" means: if necessary, add water, extracted with dichloromethane, diethyl ether or toluene, separated, dried the organic phase, evaporated and the product is purified Distillation under reduced pressure or crystallization and / or Chromatography. The following abbreviations are used:

DMEU 1,3-dimethyl-2-imidazoldinon KOT Potassium tertiary butoxide THF tetrahydrofuran pTsOH p-toluenesulfonic acid

example 1

Step 1.1

0.18 mol of trimethylsilylacetylene and 0.18 mol of 4-trans- (4-propylcyclohexyl) Bromobenzene are dissolved in 120 ml of piperidine and added portionwise with 0.3 g Tetrakis (triphenylphosphine) palladium (0). After adding 0.15 g of triphenylphosphine and 0.1 g of copper (I) iodide are slowly heated. Measure allowed to reflux for 1.5 h and then poured onto the suspension an HCl / ice water mixture. After extraction with methyl tert. butyl ether is worked up as usual.

Step 1.2

0.18 mol of KOH are dissolved in 255 ml of methanol, with the product from Step 1.1 (0.18 mol) and stirred for 1 h at room temperature. To Add 30 ml conc. HCl and 300 ml H₂O is mixed several times with methyl tert. Butyl ether extracted and then worked up as usual.

Step 1.3

0.06 mol of 1- [4- (trans-4-propylcyclohexyl) phenylacetylene, 0.06 mol of 5- Bromo-2-fluoropyrimidine and 40 ml of triethylamine are charged and touched. One after another 0.1 g of bis (triphenylphosphine) palladium (II) chloride, 0.05 g of triphenylphosphine and 0.03 g of copper (I) iodide. The mixture is stirred at room temperature for 48 h and the mixture is poured into 100 ml 2N HCl acidified ice water. After extraction with methyl tert. butyl ether is worked up as usual. K 113 N 180.3 l, Δε = 20.5; Δn = 0.268.

Analogously, the following compounds of the formula

manufactured:

Example 2

0.0074 mol of sodium and 30 ml of ethanol are stirred and treated at 50 ° C with 30 ml of ethanol and 0.0074 mol of Chlorpyrimidinderivats from Example 1. The mixture is stirred overnight at 50 ° C, allowed to cool to room temperature len and concentrated in vacuo. The residue is mixed with 100 ml of water ver and repeatedly with methyl tert. Butyl ether extracted. The combined extracts are washed with water and worked up as usual.
k 102 S _B 105 S _A 124 N 216.3 l; Δε = 6.1; Δn = +0.290.

Analogously, the following compounds of the formula

manufactured:

Claims (11)

1. The present invention relates to pyri (mi) din derivatives of the formula I, wherein
R is an unsubstituted or substituted by CN, halogen or CF₃ alkyl or alkenyl radical having up to 15 carbon atoms, wherein in these radicals also one or more CH₂ groups each independently by -O-, -CO-, -CO -O-, -O-CO or -O-CO-O- may be replaced so that O atoms are not directly linked to one another,

• a) trans-1,4-cyclohexylene radical, in which also one or more non-adjacent CH₂ groups can be replaced by -O- and / or -S-,
• b) 1,4-phenylene radical, in which also one or two CH groups can be replaced by N,
• c) radical from the group consisting of 1,4-cyclohexylene, 1,4-bicyclo [2.2.2] octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1, 2,3,4-tetrahydronaphthalene-2,6-diyl,

where the radicals (a) and (b) can be substituted by one or two fluorine,
X is alkyl or alkoxy having 1-10 C atoms, or QY, where
Q is -O-, -S- or a single bond
Y is H, F, Cl, CN, mono- or polyhalogenated alkyl or alkenyl having up to 10 C atoms,
ZN or CH
L 1 and L 2 are each independently H or F, and
m 0, 1 or 2
mean. 2. Pyrimidine derivatives of the formula wherein R, X, L¹, L² and m have the meaning given in claim 1. 3. Pyri (mi) din derivatives according to claim 1, wherein X, F, Cl, OCF₃, CF₃, CN, OCH₂CF₃ or alkoxy having 1 to 7 carbon atoms. 4. Pyri (mi) din derivatives according to claim 1, wherein m = 1. 5. Pyri (mi) din derivatives according to claims 1-4, characterized characterized in that L¹ and L² signify fluorine.   6. Pyrimidine derivatives of the formula I1 wherein R, X, L¹ and L² have the meaning given in claim 1. 7. Use of compounds of the formula I as components liquid-crystalline media. 8. Liquid-crystalline medium with at least two liquid-crystalline Components, characterized in that there is at least one Contains compound of formula I. 9. Liquid crystal display element, characterized in that it is a Liquid-crystalline medium according to claim 8 contains. 10. Electro-optical display element, characterized in that it as a dielectric liquid-crystalline medium according to claim 8 contains.