DE4110094A1 - New phenyl-ethane cpds. contg. 2 or 3 other rings - Google Patents

Abstract

New phenylethane cpds. (I) contg. 2 or 3 other trans-1,4-cyclohexylene and/or (substd.) 1,4-phenylene rings are of the formula: n = 1-7; r = 1 or 2; rings A, B and C independently = trans-1,4-cyclohexylene, 1,4-phenylene or 3-fluoro-1,4-phenylene and ring C may also = 3,5-difluoro-1,4-phenylene; s = 1 or if C = 3,5-difluoro-1,4-phenylene or B = 3-fluoro-1,4-phenylene, s may also = 0; X = F, Cl, CF3, OCF3 or OCHF2; Y and Z independently = H or F. (I) can be prepd. by standard methods, e.g. as described in Houben-Weyl, Methoden der Organischen Chemie, Georg-Thieme-Verlag, Stuttgart.

Description

The invention relates to novel phenylethanes of the formula I.

wherein n is 1 to 7, r is 1 or 2, the rings A, B and C respectively independently of each other trans-1,4-cyclohexylene, 1,4-phenylene or 3-fluoro-1,4-phenylene, ring C also 3,5-difluoro-1,4-phenylene, s 1 or in the case of C = 3,5-difluoro-1,4-phenylene or B = 3-fluoro-1,4-phenylene also 0, X F, Cl, -CF₃, -OCF₃ or -OCHF₂ and Y and Z each independently represent H or F.

From DE-OS 37 34 116 liquid crystals of the formula A are

in which R is alkyl.

The compounds A, however, are characterized only by a moderate dielectric anisotropy, which often increases in mixtures leads to relatively high threshold voltages.  

The compounds of formula I may be similar to, for. B. off DE-OS 33 17 597 known compounds as components liquid-crystalline media are used, in particular for Ads based on the principle of the twisted cell.

The substances previously used for this purpose own all certain disadvantages, for example too high melting points, too low clearing points, too little stability the effect of heat, light or electric fields, too low electrical resistance, too high temperature dependence the threshold voltage.

Especially for displays of supertwist type (STN) with twist angles significantly higher than 220 ° C or in displays with active matrix show the materials used so far Disadvantages.

The invention was based on the object, new liquid crystalline Find compounds that are components of liquid-crystalline Media are suitable, especially for nematic Positive dielectric anisotropy media, and the the disadvantages of the known compounds not or only in show a lesser degree. This task has been provided by the new compounds of formula I solved.

It has been found that the compounds of the formula I are excellent suitable as components of liquid-crystalline media are. In particular, they are liquid crystalline with their help Media with wide nematic ranges, high clearing point,  excellent nematogeneity down to low temperatures, excellent chemical stability, pronounced ε┴ at positive dielectric anisotropy, low temperature dependence the threshold voltage and / or smaller optical Anisotropy available. The new links also show a good solubility for other components of such Media and high positive dielectric anisotropy at at the same time favorable viscosity.

The compounds of formula I allow both STN displays with very high slope of the electro-optical characteristic as also displays with active matrix with excellent long-term stability.

The compounds of the formula I are colorless in the pure state and form liquid crystalline mesophases in one for the Electro-optical use conveniently located temperature range.

The invention thus relates to the compounds of Formula I and the use of the compounds of formula I. as components of liquid-crystalline media, liquid-crystalline Media containing at least one compound of the formula I and electro-optical displays, the like Media included.

Above and below n, r, s, A, B, C, X, Y and Z have the given meaning, unless expressly otherwise is noted.  

In the compounds of the formula I, the alkyl groups C _n H _{2n + 1 are} preferably straight-chain. Accordingly, C _n H _{2n + 1 is} methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl or n-heptyl. n is preferably 2, 3, 4 or 5.

Compounds of the formula I with branched alkyl groups can occasionally because of a better solubility in the usual of liquid-crystalline base materials, but especially as chiral dopants, if they are optical are active. Branched groups of this kind contain in the Usually not more than one chain branch. preferred branched alkyl radicals are isopropyl, 2-butyl (= 1-methyl) propyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl or 2-heptyl (= 1-methylhexyl).

The rest

is preferable

X is preferably F, Cl, -CF₃ or -OCF₃.  

Particularly preferred are the compounds of the following Sub-formulas:

Of the compounds of the preferred partial formulas Ia, Ie and Ig are particularly preferred where Y = F and in particular those in which Y = Z = F.  

Incidentally, the compounds of the formula I are per se prepared methods known in the literature (For example, in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg Thieme Verlag, Stuttgart) are, under reaction conditions, for the mentioned reactions are known and suitable. It can one also from known, not mentioned here Make use of variants.

If desired, the starting materials may also be in situ be formed, such that they are from the reaction mixture not isolated but immediately further to the compounds of Formula I implements.

The compounds of the formula I can, for example, by Reaction of an aldehyde of the formula

with a phosphonium salt of the formula II

after Wittig and catalytic hydrogenation z. B. to Pd / C of obtained ethene derivatives are obtained.

In formula II, q represents 1 or 3.  

The compounds of formula II are obtainable by saponification the known nitriles of the formula

Reduction to methyl alcohol and conversion to the corresponding Iodides according to routine methods. The connections with q = 3 can be prepared by mixing the iodides of a Chain extension according to routine methods (-CH₂J → CH₂CN → CH₂COOH → CH₂CH₂OH → (CH₂) ₂J etc.).

The bromobenzene derivatives used as starting materials (Scheme 1) are known in part, in part they can without difficulty according to standard methods of organic chemistry from literature Connections are made. For example are the OCF₃- or OCHF₂ compounds according to known Process from the corresponding phenols or the CF₃- or CN compounds from the corresponding benzoic acids available. Compounds of the formula

or also corresponding monofluorinated compounds for example, from the known precursors with X = H by Lithiation at low temperatures and subsequent reaction available with a suitable electrophile.  

Further synthesis variants are known to the person skilled in the art. preferred Variants are shown in Scheme 1. All starting materials are either known or can by analogy be prepared to known compounds.

Scheme 1

Scheme 2

The styrene precursor in turn is also light in one corresponding bromine or iodobenzene derivative to Heck- Pd-catalyzed coupling of the organozinc compound with Vinyl bromide available.

Inventive compounds with Y = F can, for. B. produced be prepared by reacting a compound of formula II,

wherein R

means according to the following Reaction scheme metallized and then with a suitable Electrophilic converts:

Scheme 1

From the resulting phenol are the target products with X = OCF₃ or OCHF₂ by known methods, for. B. by reaction with Chlorodifluoromethane or carbon tetrachloride / HF available.

Other synthetic methods will be apparent to those skilled in the art. For example, in the 5-position correspondingly substituted 1,3-difluorobenzene compounds or monofluorinated analogs (Z = H) according to the above scheme in the 2-OCF₂Y'-1,3-difluoro compounds (Y '= H or F) or monofluorinated Analogs (Z = F) are converted and the radical R- (C₂H₄) _r then by customary in liquid crystal chemistry reactions (eg, esterification, etherification or couplings, for example, according to the article E. Poetsch, contacts (Darmstadt) 1988 (2), p. 15).

Scheme 2

The compounds of the formula I according to the invention, wherein Z is F and X is CF₃, can be by metalation of the unsubstituted 3,5-Difluorophenylverbindungen with n-BuLi, subsequent Reaction with iodine and reaction of the iodine compound with trifluoroacetic acid sodium salt according to the following scheme produce:

The compounds of the invention with Z = H and X = CF₃ can be prepared by converting 3-fluoro-4-iodobromobenzene with CF₃COONa in the Benzotrifluoridverbindung and then the radical R- (C₂H₄) _r z. B. introduces conventional coupling reactions.

The compounds of the formula II can be, for example, according to following synthesis schemes are prepared:

Scheme 3 A = (C₂H₄) _r-1

The starting materials are either known or can be used in Be prepared analogously to known compounds.

The synthesis of some particularly preferred compounds is specified in the following:  

Scheme 4

In a further process for the preparation of the compounds of formula I is reacted with an aryl halide with an olefin in the presence of a tertiary amine and a palladium catalyst (see R.F. Heck, Acc. Chem. Res. 12 (1979) 146). Suitable aryl halides are, for example, chlorides, Bromides and iodides, especially bromides and iodides. The for the success of the coupling reaction required tertiary Amines, such as As triethylamine, are also suitable as a solvent. As palladium catalysts are, for example, the Salts, in particular (Pd (II) acetate, with organic phosphorus (III) - Connections such. B. triarylphosphines suitable. One can do this in the presence or absence of an inert Solvent at temperatures between about 0 ° and 150 °, preferably between 20 ° and 100 °, work; as a solvent come z. As nitriles such as acetonitriles or hydrocarbons such as benzene or toluene into consideration. The as starting materials used aryl halides and olefins  often available commercially or can be known from the literature Process are prepared, for example by Halogenation of corresponding parent compounds or by Elimination reactions with corresponding alcohols or Halides.

In this way, for example stilbene derivatives can be produced. The style levels can still be made by Reaction of a 4-substituted benzaldehyde with a corresponding phosphorylide according to Wittig. But you can also Formula I tolans are made by replacing the olefin monosubstituted acetylene (Synthesis 627 (1980) or Tetrahedron Lett. 27, 1171 (1986).

Furthermore, for the coupling of aromatic aryl halides with Aryltin compounds are reacted. These are preferred Reactions with the addition of a catalyst such. B. one Palladium (0) complex in inert solvents such as hydrocarbons at high temperatures, eg. B. in boiling Xylene, carried out under protective gas.

Couplings of alkynyl compounds with aryl halides can be analogous to that of A.O. King, E. Negishi, F.J. Villani and A. Silveira in J. Org. Chem. 43, 358 (1978) Procedures are performed. Catalytic hydrogenations These materials lead to the compounds of the invention.

The compounds of the formula I where r = Z can be prepared according to the following Scheme to be made:  

In the Pd (II) -catalyzed coupling reaction, either directly the target product I formed or a precursor, in this is completely analogous to the above methods for compounds or Formula I, the radical X is introduced.

The compounds of the formula I can furthermore according to Wittig according to the following scheme:  

The preferred trans isomers may be prepared according to known from the literature isomerization methods. The optionally obtained precursors with R⁰ = H are completely analogously to the precursors of the compounds of the formula I. by introducing the radical X into the compounds of the formula I transferred.

The aldehydes can be converted by Heck reaction from accordingly substituted 1-bromo-3-fluorobenzene derivatives with allyl alcohol to be obtained.

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. Very particularly preferably included these media in addition to one or more inventive Compounds 7 to 25 components. These other ingredients are preferably selected from nematic or  nematogenic (monotropic or isotropic) substances, in particular Substances from the classes of biphenyls, terphenyls, Phenyl or cyclohexyl benzoates, cyclohexane-carboxylic acid phenyl or cyclohexyl esters, phenyl or cyclohexyl esters the cyclohexylbenzoic acid, phenyl or cyclohexyl ester of Cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl ester of Benzoic acid, cyclohexanecarboxylic acid or cyclohexylcyclohexanecarboxylic acid, Phenylcyclohexanes, cyclohexylbiphenyls, Phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, Cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4'-biscyclohexylbiphenyls, Phenyl or cyclohexylpyrimidines, phenyl or cyclohexylpyridines, Phenyl or cyclohexyl dioxanes, phenyl or cyclohexyl 1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4- phenylcyclohexyl) ethanes, 1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes and tolans.

The 1,4-phenylene groups in these compounds can also be fluorinated.

The most important as further constituents according to the invention Media eligible connections can be through 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 are the same or may be different, each independently a bivalent radical from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc, -Cyc-Cyc, -Pyr-, -Dio, -G-Phe- and -G-Cyc- and whose mirror images formed a group, with Phe unsubstituted or fluorine-substituted 1,4-phenylene, Cyc trans-1,4-cyclohexylene or 1,4-cyclohexenylene, Pyr pyrimidine 2,5-diyl or pyridine-2,5-diyl, dio-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 included the media of the invention one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein L and E are selected from the group Cyc, Phe and Pyr and at the same time selected one or more components from the compounds of the formulas 1, 2, 3, 4 and 5, wherein one of 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 the compounds of the formulas 1, 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 the compounds of sub-formulas 1a, 2a, 3a, 4a and 5a are each independently of one another alkyl, Alkenyl, alkoxy, alkenyloxy or alkanoyloxy with up to 8 Carbon atoms. For most of these compounds are  R 'and R' 'different from each other, wherein one of these radicals usually alkyl or alkenyl. In the compounds of the sub-formulas 1b, 2b, 3b, 4b and 5b represents R "-CN, -CF₃, -OCF₃, F, Cl or -NCS; R has the same in the compounds of the sub-formulas 1a to 5a, and is preferred Alkyl or alkenyl. More preferably, R "is selected from the group consisting of -F, Cl, CF₃ and -OCF₃. But also other variants of the proposed substituents in the compounds Formulas 1, 2, 3, 4 and 5 are common. Many such substances or mixtures thereof are in the Trade available. All these substances are known from the literature Methods or by analogy.

The media according to the invention preferably contain in addition Components from the group of compounds 1a, 2a, 3a, 4a and 5a (Group 1) also components from the group of compounds 1b, 2b, 3b, 4b and 5b (group 2), their proportions preferably as follows:

Group 1: 20 to 90%, in particular 30 to 90%,
Group 2: 10 to 80%, in particular 10 to 50%,

wherein the sum of the proportions of the compounds of the invention and the compounds from groups 1 and 2 up to 100% result.  

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 inventive Links. The media preferably contain three, four or five compounds of the invention.

The preparation of the media according to the invention takes place in usual way. In general, the components are dissolved in each other, useful at elevated temperature. By Suitable additives can after the liquid crystalline phases of the invention are modified so that they are in all hitherto have become known types of liquid crystal display elements can be used. Such additives are those skilled in the art known 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 of colored guest host systems or substances for changing the dielectric anisotropy, the Viscosity and / or the orientation of the nematic phases be added.

The following examples are intended to illustrate the invention, without to limit them. mp = melting point, cp. = clearing point. In front- and below, percentages are by weight; all Temperatures are given in degrees Celsius. "Usual work-up" means: you add water, extracted with Methylene chloride, separates, the organic phase dries, Evaporates and purifies the product by crystallization and / or chromatography.  

It also means:
K: crystalline solid state,
S: smectic phase (the index indicates the phase type),
N: nematic state,
Ch: cholesteric phase,
I: isotropic phase.
The number between two symbols indicates the transformation temperature in degrees Celsius.

DAST diethylaminosulfur DCC dicyclohexylcarbodiimide DDQ dichlorodicyanobenzoquinone DIBALH diisobutylaluminum DMSO dimethyl sulfoxide KOT Potassium tert-butoxide THF tetrahydrofuran pTSOH p-toluenesulfonic acid

Example 1

After hydrogenation of 1- [p- (trans-4- (trans-4-n-propylcyclohexyl) - cyclohexyl) -phenyl] -2- (3,4-difluorophenyl) -ethene (prepared according to Scheme 1) on Pd-C at room temperature and usual workup gives 1-p- (trans-4-n- Propylcyclohexyl) -cyclohexyl) phenyl) -2- (3,4-difluorophenyl) - ethane.  

Example 2 to 28

Analogously to Example 1, the following compounds are obtained Partial Formula Ia:

example 29

A mixture of 10.5 g of 1-bromo-3,4-difluorobenzene, 17.4 g 4- (trans-4-propylcyclohexyl) -2,6-difluorostyrene (available to Int. Patentanm. No. PCT / EP 90/02 109), 0.25 g of Pd acetate, 0.6 g of tri-o-tolylphosphine, 7 g of triethylamine and 125 ml of acetonitrile is heated to reflux until the reaction is complete. After customary workup, trans-1- (3,4-difluorophenyl) - 2- [4- (trans-4-propylcyclohexyl) -2,6-difluorophenyl] - ethene (K 101 N 156.5 I). A solution of 2.6 g of this Compound in 30 ml of tetrahydrofuran is mixed with 0.7 g of Pd-C (5%) added and hydrogenated at a slight overpressure. You get 1- (3,4-difluorophenyl) -2- [4- (trans-4-propylcyclohexyl) -2,6- difluorophenyl] ethane.

Analogously to Example 28, the following compounds are obtained Partial formula Ig:

example 30

A solution of 0.1M 1- (4-n-propyl-2-fluorobiphenyl-4'-yl) - 2- (3,5-difluorophenyl) ethane (prepared according to WO 90/08 757) and 0.1 M TMEDA in 300 ml of THF at about -65 ° with 0.1 m n-BuLi (1.5 M in hexane) was added dropwise. Man is still stirring 30 min at this temperature and added dropwise at -60 to -70 ° C. 0.1 m B (OCH₃) ₃. It is stirred for 1/2 h. Then you drip 0.3 m H₂O₂ (30%), the temperature + 40 ° C not should exceed. After extractive workup you get the phenol which is obtained by crystallization or distillation can be cleaned.

From this phenol obtained OCHF₂ derivative by introduction of CHClF₂ in the THF solution of the phenolate. After extractive Work-up and customary purification gives 1- (4-n-propyl) 2-fluorobiphenyl-4'-yl) -2- (4-difluoromethoxy-3,5-difluorophenyl) - ethane.

example 31

In an autoclave, which is cooled to 0 °, it is filled 2 mol anhydrous hydrofluoric acid. Then you give out a mixture 0.18 mol of tetrachloromethane and 0.06 mol of 1- (4-n-propyl-2-fluorobiphenyl) 4'-yl) -2- (4-hydroxy-3,5-difluorophenyl) -ethane (Example 30). The mixture is stirred for about 8 hours at 150 °, cooled, poured onto ice-water and washed with ether. The two phases are stirred for about 30 minutes,  separated and the ether solution with 5% KOH to alkaline Reaction washed. After drying, filtration, distilling off and purification gives 1- (4-n-propyl-2-fluorobiphenyl- 4'-yl) -2- (4-trifluoromethoxy-3,5-difluorophenyl) -ethane.

example 32

A solution of 0.1M 1- (4-n-propyl-2-fluorobiphenyl-4'- yl) -2- (3,5-difluorophenyl) ethane (prepared according to Scheme 3) and 0.1 M TMEDA in 300 ml of THF at about -65 ° C with 0.1 m n-BuLi (1.5 M in hexane) was added dropwise. Man is still stirring 30 min. At this temperature and then sets 0.2 m N-chlorosuccinimide in 70 ml THF slowly too. After the end of the addition allowed to warm to -20 ° and hydrolyzed with H₂O. By Addition of diethyl ether will completely dissolve the product Solution brought. After extractive workup and cleaning Chromatography and crystallization give 1- (4-n- Propyl-2-fluorobiphenyl-4'-yl) -2- (4-chloro-3,5-difluorophenyl) - ethane.

example 33

A mixture of 0.025 m CuJ, 0.0125 m CF₃COONa and 0.0125 m 1- (4-n-propyl-2-fluorobiphenyl-4'-yl) -2- (4-iodo-3,5-difluorophenyl) - ethane [available according to Scheme 15] is dissolved in 100 ml Heated N-methylpyrrolidone with stirring to 150 °. After a Hour you work up as usual extractive and get after Chromatographic purification 1- (4-n-propyl-2-fluorobiphenyl- 4'-yl) -2- (4-trifluoromethyl-3,5-difluorophenyl) -ethane.  

example 34

37.1 g of I (0.1 mol) are dissolved in 150 ml of a solvent mixture of THF / toluene (1: 4 volume ratio), then 11.5 g of zinc bromide anhydrous and then 1.4 g Added lithium granules. The mixture is under argon and stirring for 4 hours between 0 ° C and 10 ° C with ultrasound treated I to the corresponding dialkylzinc compound to convict. The organozinc compound is 21.1 g II (0.1 mol) and 1.5 g (2 mol%) of 1,1'-bis (diphenylphosphine) - ferrocene-palladium (II) dichloride (PdCl₂ dppf) and After removal of the ultrasonic bath and cooling 24 h stirred at room temperature. It is saturated with 100 ml NH₄Cl solution decomposed with stirring, the organic phase separated, the aqueous phase extracted 2 × with toluene. The combined organic extracts provide after the Dry, concentrate and chromatograph on silica gel with Hexane III. (I can be prepared by chain extension of:

using malonate.)  

example 35

37.1 g (100 mmol) of 1 are converted analogously to Example 207 by reaction with 2 in 3 .

To a mixture of 19.0 g (47 mmol) of 3 7.5 ml of TMEDA (50 mmol) and 150 ml of THF are added dropwise at -65 to -70 ° C 31 ml of n-BuLi (15% in hexane) and it is Stirred at -70 ° C for 1 hour. Then, a solution of 12.0 g (47 mmol) of iodine in 25 ml of THF is added dropwise at -65 to -70 ° C and stirred at -70 ° C for 0.5 h. The mixture is warmed to -30 ° C, hydrolyzed with 15 ml of water and reduced excess iodine by adding 15 ml of sodium bisulfite solution. After customary work-up and recrystallization from hexane, 23.9 g (45 mmol) of 4 are obtained . From a mixture of 20.2 g (38 mmol) of 4 , 4.4 g (76 mmol) of KF, 22.8 g (168 mmol) of sodium trifluoroacetate and 800 ml of NMP 400 ml of NMP are distilled off at 70 ° C and 4 mbar. Then, 14.4 g (76 mmol) of dried CuJ are added to the reaction mixture and the mixture is stirred at 160 ° C. for 5 h. Subsequently, about 300 ml of NMP are distilled off. It is allowed to cool to RT and mixed with 300 ml of MTB ether. It is washed with water, dried with Na₂SO₄, filtered and concentrated to the residue. After chromatography on silica gel with hexane to obtain 5 .

The following are some particularly preferred compounds the partial formula Ie stated:

as well as those of the partial formula Ig

as well as those of the preferred partial formula If

Claims (11)

1. phenylethanes of the formula I. where n is 1 to 7, r is 1 or 2, the rings A, B and C are each, independently of one another, trans-1,4-cyclohexylene, 1,4-phenylene or 3-fluoro-1,4-phenylene, ring C also 3, 5-difluoro-1,4-phenylene, s 1 or in the case of C = 3,5-difluoro-1,4-phenylene or B = 3-fluoro-1,4-phenylene also 0, XF, Cl, -CF₃, -OCF₃ or -OCHF₂ and Y and Z are each independently H or F. 2. Phenylethanes according to claim 1, characterized by the formula Ia wherein n, X, Y and Z have the meaning given. 3. Phenylethanes according to claim 1, characterized by the formula Ib 4. Phenylethanes according to claim 1, characterized by the formula Ic wherein n, X, Y and Z have the meaning given. 5. phenylethanes according to claim 1, characterized by the formula Id wherein n, X, Y and Z have the meaning given. 6. phenylethanes according to claim 1, characterized by the formula Ie wherein n, r, X, Y and Z have the meaning given. 7. phenylethanes according to claim 1, characterized by the formula If wherein n, X, Y and Z have the meaning given. 8. phenylethanes according to claim 1, characterized by the formula Ig wherein n, s, r, X, Y and Z have the meanings indicated. 9. Use of the phenylethanes of the formula I according to claim 1 as components of liquid-crystalline media for electro-optical Show. 10. Liquid-crystalline medium for electro-optical displays with at least two liquid crystalline components, characterized in that at least one component a phenylethane of the formula I according to claim 1. 11. Electro-optical display based on a liquid crystal cell, characterized in that the liquid crystal cell contains a medium according to claim 10.