DE19818461A1 - New oligo-1,3-dioxan derivatives - Google Patents

Abstract

Oligo-1,3-dioxan derivatives of formula (I) are claimed. In (I), R<1>, R<2> = 1-12C alkyl or alkenyl (optionally substituted with one CN or CF3 or with at least one halogen and optionally with one or more CH2 groups replaced by O, S, CO, COO, OCO or OCOO with no direct link between hetero atoms); R<2> may also = F, Cl or CN; A<1>, A<2> = (a) trans-1,4-cyclohexylene (Cyc) in which one or more non-adjacent CH2 groups may be replaced by O and/or S, (b) 1,4-cyclohexenylene, (c) 1,4- phenylene (Pn) in which 1 or 2 CH groups may be replaced by N, or (d) 1,4-bicyclo2.2.2octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl or its decahydro or 1,2,3,4-tetrahydro derivatives, in which groups (a), (b) and (c) may also be substituted with CN or F; Z<1>, Z<2> = COO, OCO, CH2O, OCH2, CH2CH2, CH=CH, C?=C or a single bond; m, n = 0 or 1; m + n = 0 or 1; if A<2> = Cyc, n = 1 and R<2> = -O-CH=CXY (in which one of the groups X, Y is H, F or Cl and the other is F or Cl), then Z<2> = COO, OCO, CH2O, OCH2, CH2CH2, CH=CH or C?=C.

Description

The invention relates to oligo-1,3-dioxane derivatives of the general formula I.

wherein
R ¹ and R ² each independently of one another are an unsubstituted, an alkyl or alkenyl radical with 1 to 12 carbon atoms which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, one or more CH ₂ groups in each of these radicals can be replaced independently of one another by -O-, -S-, -CO-, -CO-O-, -O-CO- or -O-CO-O- in such a way that heteroatoms are not directly linked to one another,
R ² also F, Cl or CN,
A ¹ and A ² each independently

• a) trans-1,4-cyclohexylene radical, in which one or more non-adjacent CH ₂ groups can also be replaced by -O- and / or -S-,
• b) 1,4-cyclohexenylene radical,
• c) 1,4-phenylene radical, which also includes one or two CH groups can be replaced by N,  
• d) radical from the group 1,4-bicyclo (2,2,2) octylene, Piperidine-1,4-diyl, naphthalene-2,6-diyl, deca hydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydro naphthalene-2,6-diyl,

where the residues a), b) and c) can be substituted by CN or F,
Z ¹

and Z ²

each independently of the other -CO-O-, -O-CO-, -CH ₂

O-, -OCH ₂

-, -CH ₂

CH ₂

-, -CH = CH-, -C∼C- or a single bond, and
m and n are each independently 0 or 1,
where m + n = 0 or 1,
mean,
with the proviso that
if A ²

1,4-cyclohexylene, n 1 and R ²

is in which one of the radicals X and Y is H, F or Cl and the other is F or Cl, Z ² -COO-, -OCO-, -CH ₂ O-, -OCH ₂ -, -CH ₂ CH ₂ -, - CH = CH- or -C∼C- is.

The invention further relates to a process for the preparation of the oligo- 1,3-dioxane derivatives of the general formula I *

wherein
R ¹ , R ² , A ¹ , A ² , Z ¹ and Z ^{2 have} the meaning given in claim 1,
m * and n * are each independently 0, 1 or 2, and
p * 1 or 2,
where m * + n * + p * = 2, 3 or 4,
mean,
with the provisos that
(a) when p * 2, A ² 1,4-cyclohexylene, n * 1 and R ²

is in which one of the radicals X and Y is H, F or Cl and the other is F or Cl, Z ² -COO-, -OCO-, -CH ₂ O-, -OCH ₂ -, -CH ₂ CH ₂ -, - CH = CH- or -C∼C-,
and
(b) when R ²

where X ¹ and X ² each independently represent H, F or Cl, p * 2,
the intermediates passed through this process and the use of the oligo-1,3-dioxane derivatives of the general formula I as components of liquid-crystalline media and liquid-crystal and electro-optical display elements which contain the liquid-crystalline media according to the invention.

The compounds of formula I can be liquid crystalline as components Media are used, especially for displays based on the principle the twisted cell, the guest-host effect, the effect of the deformation aligned phases or the effect of dynamic scattering are based.

The invention was based on the object, new stable liquid-crystalline or to find mesogenic compounds that are liquid as components crystalline media are suitable and, in particular, at the same time comparatively high dielectric anisotropy Δε as well as a very have low optical anisotropy Δn.

It has now been found that compounds of the formula I as components liquid crystalline media are particularly suitable. In particular, have they have comparatively high dielectric anisotropies Δε at the same very low optical anisotropies Δn. With their help stable liquid-crystalline media with a wide mesophase range and above obtained partial values for the optical and dielectric anisotropy. These media also have very good low-temperature behavior.

Liquid crystalline di-1,3-dioxane derivatives are already known.

EP 0 732 330 A1 describes 1,3-dioxanes of the formula

claimed, wherein A and B are independently cyclic or mean acylic hydrophobic radicals and n is 0.1 or 2, and their Use in liquid crystal mixtures.

In DE 195 25 314.0, dioxanyl dioxanes containing a structural element of the formula

claimed, wherein A is -CH ₂ CH ₂ -, -CH = CH-, -C∼C- or 1,4-cyclo hexylene and m is 0 or 1, and a process for their preparation.

The compound disclosed in EP 0 732 330 A1 and DE 195 25 314.0 with two directly linked 1,3-dioxane-2,5-diyl groups obtained by condensation of diols with carbonyl compounds.

With regard to the various areas of application of 1,3-dioxanes high Δε, however, it was desirable to have other compounds with high To have nematogenicity available that is appropriate for the respective application precisely tailored properties.

With the provision of compounds of oligo-1,3-dioxane derivatives Formula I will also generally be the range of liquid crystalline Substances that can be found under different application technology Are suitable for the production of liquid crystalline mixtures, significantly broadened. The compounds of formula I have one wide scope. Depending on the selection of the Substituents these compounds can serve as base materials, from which liquid-crystalline media for the most part are composed; however, compounds of the formula can also be used liquid-crystalline base materials from other classes of compounds can be added, for example, the dielectric and / or optical To influence anisotropy of such a dielectric and / or to optimize its threshold voltage and / or its viscosity. The Compounds according to the invention are particularly notable for their wide mesophase range at very low values for the optical anisotropy Δn and relatively high values for the dielectric Anisotropy Δε off.  

The compounds of the formula I are colorless in the pure state and form liquid crystalline mesophases in one for electro-optical use conveniently located temperature range. Chemical, thermal and against Light they are stable.

The invention thus relates to the oligo-1,3-dioxane derivatives Formula I, a process for the preparation of the oligo-1,3-dioxane derivatives Formula I * and the new intermediates passed through this process products as well as the use of the oligo-1,3-dioxane derivatives of Formula I as components of liquid crystalline media. Subject of Invention are also liquid crystalline media containing at least one oligo-1,3-dioxane derivative of the formula I and Liquid crystal display elements, in particular electro-optical Display elements that contain such media.

Another object of the invention is a process for the preparation of the oligo-1,3-dioxane derivatives of the formula I *, wherein a bis-silyl ether of the general formula II *

wherein
R ¹ , A ¹ and Z ^{1 have} the meaning given in claim 1,
m * 0, 1 or 2,
p * 1 or 2, and
R ^a , R ^b and R ^c each independently represent an alkyl radical having 1 to 6 carbon atoms or an aryl radical,
with an aldehyde of the formula OHC- (Z ² -A ² ) _{n *} -R ² ,
wherein
R ² , A ² and Z ^{2 have} the meaning given in claim 1, and
n * 0, 1 or 2
means
condensed.

The invention furthermore relates to new bis-silyl ethers of the general formula II *

wherein
R ¹ , A ¹ and Z ^{1 have} the meaning given in claim 1,
m ** 0 or 1, and
R ^a , R ^b and R ^c each independently represent an alkyl radical having 1 to 6 carbon atoms or an aryl radical.

The invention further relates to a process for the preparation of oligo-1,3-dioxane derivatives of the general formula I *, the bis-silyl ether of the general formula II * being etherified by etherification of a diol of the general formula III *

wherein
R ¹ , A ¹ and Z ^{1 have} the meaning given in claim 1,
m * 0, 1 or 2, and
p * 1 or 2
mean,
with a silyl halide of the formula HalSiR ^a R ^b R ^c ,
wherein
R ^a , R ^b and R ^c each independently of one another are an alkyl radical having 1 to 6 carbon atoms or an aryl radical, and
Hal Cl, Br or I
mean,
manufactures.

The invention furthermore relates to a process for the preparation of oligo-1,3-dioxane derivatives of the general formula I *, the bis-silyl ether of the general formula II *
(a) with an aldehyde of the formula

wherein
Bn is a benzyl group in which the phenyl ring can also be substituted by alkyl, alkoxy, halogen, CN, NO ₂ or NH ₂ ,
means
is condensed
(b) the condensation product is reduced, and
(c) the reduction product with a silyl halide of the formula HalSiR ^a R ^b R ^c ,
wherein
R ^a , R ^b and R ^c each independently of one another are an alkyl radical having 1 to 6 carbon atoms or an aryl radical, and
Hal Cl, Br or I
mean,
is reacted, and the reaction product is then reacted with an aldehyde of the formula OHC- (Z ² -A ² ) _{n *} -R ² ,
wherein
R ² , A ² and Z ^{2 have} the meaning given in claim 1,
and
n * 0, 1 or 2
means
is condensed.

Another object of the invention are aldehydes of the formula

wherein
Bn is a benzyl group in which the phenyl ring can also be substituted by alkyl, alkoxy, halogen, CN, NO ₂ or NH ₂ ,
means.

Above and below, R ¹ , R ² , Z ¹ , Z ² , A ¹ , A ² , m, n, m *, n *, p * and m ** have the meaning given, unless expressly stated otherwise .

For the sake of simplicity, Cyc ^a in the following means a 1,4-cyclohexylene radical, Che a 1,4-cyclohexenylene radical, Dio a 1,3-dioxane-2,5-diyl radical, Dit a dithiane-2,5-diyl radical, Phe ^a a 1,4-phenylene radical, Pyd a pyridine-2,5-diyl radical, pyr ^a a pyrimidine-2,5-diyl radical and Bco a bicyclo (2,2,2) octylene radical, with Cyc ^a and / or Phe ^a unsubstituted or can be substituted one or more times by F or CN.

The compounds of the formula I according to the invention comprise compounds without a ring in the mesogenic groups R ¹ - (A ¹ -Z ¹ ) _m - and - (Z ² -A ² ) _n -R ^{2 of} the sub-formula Ia:

R ¹ -Dio-Dio-Dio-R ² Ia

and compounds with a ring in the mesogenic groups R ¹ - (A ¹ -Z ¹ ) _m and - (Z ² -A ² ) _n -R ^{2 of} the sub-formulas Ib to Ie:

R ¹ -A ¹ -dio-dio-dio-R ² Ib

R ¹ - A ¹ -Z ¹ -dio-dio-dio-R ² Ic

R ¹ -Dio-Dio-Dio-A ² -R ² Id

R ¹ -Dio-Dio-Dio-Z ² -A ² -R ² Ie.

Among them, the sub-formulas Ia, Ib, Id and Ie are particularly preferred.

The preferred compounds of sub-formula Ib include those of sub-formulas Iba and Ibb:

R ¹ -Cyc ^a -Dio-Dio-Dio-R ² Iba

R ¹ -Phe ^a -Dio-Dio-Dio-R ² Ibb.

The preferred compounds of sub-formula Id include those of sub-formulas Ida to Idc:

R ¹ -dio-dio-dio-cyc ^a -R ² Ida

R ¹ -Dio-Dio-Dio-Phe ^a -R ² Idb

R ¹ -Dio-Dio-Dio-Che-R ² Idc.

Among them, those of the formulas Ida and Idb are particularly preferred.

The preferred compounds of sub-formula Ie include those of sub-formula Iea:

R ¹ -dio-dio-dio-CH ₂ CH ₂ -Phe ^a -R ² Iea.

The following compounds of the formulas I * a to I * m can also be prepared by the process according to the invention:

R ¹ -dio-dio-R ² I * a

R ¹ -A ¹ -dio-dio-R ² I * b

R ¹ -A ¹ -Z ¹ -dio-dio-R ² I * c

R ¹ -Dio-Dio-A ² -R ² I * d

R ¹ -Dio-Dio-Z ² -A ² -R ² I * e

R ¹ -A ¹ -A ¹ -dio-dio-R ² I * f

R ¹ -A ¹ -Z ¹ -A ¹ -dio-dio-R ² I * g

R ¹ -A ¹ -A ¹ -Z ¹ -dio-dio-R ² I * h

R ¹ -A ¹ -Z ¹ -A ¹ -Z ¹ -dio-dio-R ² I * i

R ¹ -dio-dio-A ² -A ² -R ² I * j

R ¹ -Dio-Dio-Z ² -A ² -A ² -R ² I * k

R ¹ -Dio-Dio-A ² -Z ² -A ² -R ² I * l

R ¹ -Dio-Dio-Z ² -A ² -Z ² -A ² -R ² I * m.

The preferred compounds of the formulas I * a to I * m include those of the following formulas:

R ¹ -dio-dio-R ² I * a

R ¹ -Cyc ^a -Dio-Dio-R ² I * ba

R ¹ -Phe ^a -Dio-Dio-R ² I * bb

R ¹ -dio-dio-Cyc ^a -R ² I * da

R ¹ -Dio-Dio-Phe ^a -R ² I * db

R ¹ -Dio-Dio-Che-R ² I * dc

R ¹ -dio-dio-CH ₂ CH ₂ -Phe ^a -R ² I * ea

R ¹ -dio-dio-Cyc ^a -Phe ^a -R ² I * yes.

The compounds of the formula II ** according to the invention include those of the sub-formulas II ** a to II ** c:

R ¹ -Dio-Dio-W II ** a

R ¹ -A ¹ -Dio-Dio-W II ** b

R ¹ -A ¹ -Z ¹ -Dio-Dio-W II ** c

where W

means and R ^a , R ^b and R ^{c have} the meaning given.

Among them, partial formulas II ** a and II ** b are particularly preferred.

The preferred compounds of sub-formula II ** b include those of sub-formulas II ** ba and II ** bb:

R ¹ -Cyc ^a -Dio-Dio-W II ** ba

R ¹ -Phe ^a -Dio-Dio-W II ** bb.

In the compounds of the formulas above and below, R preferably denotes unsubstituted straight-chain alkyl, alkenyl or oxaalkyl. R ² preferably denotes unsubstituted straight-chain alkyl or alkenyl. The alkenyl radical is preferably 1 E-alkenyl, 3E-alkenyl or 4-alkenyl. In the case where R ² is bonded to an optionally substituted 1,4-phenylene ring, R ^{2 is} preferably F, Cl, OCF ₃ , OCHF ₂ , CF ₃ , CHF ₂ , OCHFCF ₃ , OCHFCHF ₂ , OCH ₂ CF ₃ , OC ₂ F ₅ , OC ₃ F ₇ , OCF = CHF, OCF ₂ CHFCF ₃ , in particular F, OCF ₃ , OCHF ₂ , OCHFCF ₃ and OCHFCHF ₂ .

A ¹ and A ² independently of one another are preferably Phe ^a , Cyc ^a , Che, Pyd or Pyr ^a , particularly preferably Phe ^a , Cyc ^a or Che, particularly preferably Phe ^a or Cyc ^a .

A ¹ and A ^{2 are} preferably

the rings too can occur inverted.

Z ¹ and Z ^{2 are} preferably CH ₂ CH ₂ or a single bond, particularly preferably a single bond.

m and n are preferably 0.

m * and n * are each independently 0 or 1. Particularly preferably, m * and n * mean 0. p * means preferably 1.

m ** preferably means 0.

R ^a , R ^b and R ^c each preferably independently of one another denote alkyl having 1 to 4 carbon atoms or aryl, in particular methyl, ethyl, isopropyl, tert-butyl or phenyl. R ^a , R ^b and R ^{c are} all preferably methyl at the same time.

In the compounds of the formula

means Bn preferred an unsubstituted benzyl group.

If R ¹ and R ^{2 represent} 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 preferably means ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, furthermore methyl , Octyl, nonyl, decyl, undecyl, dodecyl, methoxy, octoxy, nonoxy, decoxy or undecoxy.

Oxaalkyl preferably means 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-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R ¹ and R ^{2 represent} an alkenyl radical, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it means 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-1 -, 2-, 3-, 4-, 5-, 6-, 7-, 8- or Dec-9-enyl.

If R ¹ and R ^{2 represent} an alkyl radical in which one CH ₂ group has been replaced by -O- and one has been replaced by -CO-, these are preferably adjacent. Thus, these include an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. These are preferably straight-chain and have 2 to 6 carbon atoms.

Accordingly, they mean especially acetyloxy, propionyloxy, butyryloxy, Pentanoyioxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, Butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyl oxyethyl, 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- (propoxycarbonyl) - ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl, 4- (methoxy carbonyl) butyl.  

If R ¹ and R ² represent a mono-substituted by CN or CF ₃ alkyl or alkenyl radical, this radical is preferably straight-chain and the substitution by CN or CF ₃ in ω-position.

If R ¹ and R ^{2 represent} an alkyl or alkenyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain and halogen is preferably F or Cl. In the case of multiple substitution, halogen is preferably F. The resulting residues also include perfluorinated residues. In the case of single substitution, the fluorine or chlorine substituent can be in any position, but preferably in the ω position.

Compounds of the formula I with branched wing groups R ¹ and R ² can occasionally be of importance because of their better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectic compounds of this type are suitable as components for ferroelectric materials.

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

Branched groups of this type usually contain no more than one chain branch. Preferred branched radicals R ¹ and R ² 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-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy.

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

Among these are compounds of formula I and the sub-formulas preferred those in which at least one of those contained therein Radicals has one of the preferred meanings indicated.  

Some very particularly preferred smaller groups of compounds of the formula I according to the invention are those of the sub-formulas I1 to I8:

Preferred sub-formulas of the formula I1 are the formulas I1a to I1d:

wherein alkyl is an alkyl radical having 1 to 12 carbon atoms, preferably one straight-chain unsubstituted alkyl radical with 1 to 7 carbon atoms and alkenyl an alkenyl radical having 2 to 12 carbon atoms, preferably one straight means chain-unsubstituted alkenyl radical having 2 to 10 carbon atoms.

Further preferred sub-formulas of the compounds I1b, I1c and I1d are those of the formulas I1b1, I1b2, I1c1, I1c2 and I1d1 to I1d4:

wherein q and q '1 to 7, r and r' are each independently 0 to 8 and s and s' each independently represent 0 to 6.

Preferred sub-formulas of the formulas II ** a, II ** ba and II ** bb are those formulas in which R ^{1 is} an alkyl radical with 1 to 12 C atoms, preferably a straight-chain unsubstituted alkyl radical with 1 to 7 C atoms or one Alkenyl radical having 2 to 12 carbon atoms, preferably a straight-chain unsubstituted alkenyl radical having 2 to 10 carbon atoms. Among these alkenyl residues, the 1 E-alkenyl and 3E-alkenyl residues are particularly preferred. Among the preferred sub-formulas of the formulas II ** a, II ** ba and II ** bb, those are particularly preferred in which R ^a , R ^b and R ^c all mean methyl at the same time.

The compounds of formula I are according to methods known per se presented as they are in the literature (e.g. in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart) are described, namely under reaction conditions that for the implementations mentioned are known and suitable.

You can also use known ones that are not mentioned here Make use of variants.  

The diols of the formula required as starting materials

are either known or can by known methods are produced (see e.g. DE 195 25 314.0).

The oligo-1,3-dioxane derivatives are easily accessible by the 1,3-dioxane ring by condensation of a bis-trialkylsilyl ether with a Aldehyde is formed.

Acetal synthesis based on bis-silyl ethers and carbonyl verb dungen is known per se. Suitable embodiments of this reac tion (see e.g. R. Noyori, S. Murata, M. Suzuki, Tetrahedron 1981, 37, 3899-3910; FA. Carey, R. J. Sundberg, Advanced Organic Chemistry, 3rd ed., Part B: Reactions and Synthesis, Plenum Press, NewYork, 1993, p. 689 and the literature cited there) be removed.

The implementation of the reaction of the bis-silyl ether with carbonyl connections is easy. The raw materials are under catalytic Action of Lewis acids at temperatures from + 50 ° C to -150 ° C, preferably at temperatures from -50 ° C to -100 ° C, especially preferably at temperatures from -60 ° to -90 ° C at elevated or reduced pressure, but preferably at normal pressure under good Mixing in aprotic solvents brought to implementation. The reaction is usually carried out under inert gas and by Addition of a base ended.

Commonly used Lewis acids such as aluminum or boron trihalides or tin or titanium tetrahalides, preferably BF ₃ , AlCl ₃ , SnCl ₄ or TiCl ₄ , can be used as catalysts in a homogeneous phase, but Lewis acids, which are the organic substrates, are particularly preferably used can activate via an electrophilic single-center coordination such as Lewis acids that contain silicon as the central atom. Trialkylsilyltrifluoromethanesulfonates, in particular trimethylsilyltrifluoromethanesulfonate (TMSOTf), are particularly preferred as catalysts. However, it is also possible, if possible, to advantageously use trialkylsilyl halides, preferably trimethylsilyl chlorides, bromides or iodides or else immobilized catalysts such as Nafion-TMS.

Aprotic solvents are used as organic solvents det. Halogenated hydrocarbons are particularly preferred preferably chlorinated alkanes such as dichloromethane, tri chloromethane or trichloroethane or hydrocarbons such as wise use of benzene or toluene. Is particularly preferred Dichloromethane as a solvent for the acetalization of the bis-silyl ethers with carbonyl compounds.

The choice of base is not critical. Among other things, Substan zen such as alkali or alkaline earth carbonates, and hydroxides on. However, nitrogen bases such as triethylamine and ammonia are preferred or pyridine used. A particularly preferred base is pyridine.

An embodiment of the method according to the invention is preferred, in which the starting materials bis-silyl ether and carbonyl compound in egg nem molar ratio of 1:10 to 10: 1, in particular from 1: 3 to 3: 1 stand. The starting materials are particularly preferred in almost equimolar ratio used. The amount of catalyst is bezo gene on the amount of aldehyde preferably less than 10 mol% and more than 0.001 mol%, particularly preferably less than 10 mol% and more than 0.01 mol%.

A preferred embodiment of the method according to the invention consists in the representation of the bis-silyl ether by etherification of a Diols. Silyl ethers are common protective groups for alcohols Synthesis of silyl ethers from alcohols is extensive in the literature described. Suitable embodiments of this reaction can be the Literature (see e.g. T. W. Greene, P. G. M. Wuts, Protective Groups in  Organic Synthesis, 2nd ed., John Wiley & Sons, Inc., New York, 1991, Pp. 68-86 and the literature cited there).

The bis-silyl ethers are preferably prepared by conversion tion of diols with silylating reagents such that the starting materials in a suitable solvent and at temperatures of -20 ° C to 150 ° C, preferably at temperatures from 0 ° C to 100 ° C and especially at room temperature with increased or reduced pressure, but preferably at normal pressure in the presence of a base to reak tion brings. The reaction under inert gas and good mixing of the starting materials in the presence of a catalyst carried out.

Common silyl compounds, which are advantageous in the invention Methods that can be used are, for example, alkyl, aryl or alkylarylsilyl halides, especially the corresponding silyl chloride trimethylsilyl chloride, triethylsilyl chloride triisopropylsilyl chloride, Dimethylisopropylsilyl chloride, diethylisopropylsilyl chloride, tert-butyldi methylsilyl chloride, tert-butyldiphenylsilyl chloride, triphenylsilyl chloride or Diphenylmethylsilyl chloride. Trimethylsilyl can be particularly preferred chloride can be used for the production of bis-silyl ether. There are however, other silylation reagents such as hexaalkyl disilazanes or trialkylsilyltrifluoromethanesulfonates can be used.

Aprotic solvents such as for example tetrahydrofuran, dichloromethane, acetonitrile, pyridine, N, N-dimethylformamide, hexamethylphosphoric triamide or N-methylpyrrolidone use. Particularly preferred solvents are u. a. N, N-dimethylformamide or pyridine.

Nitrogen-containing compounds are preferred as bases. Especially suitable bases are e.g. B. Compounds such as triethylamine or pyridine. However, the reaction can also be advantageous using basic ion exchangers can be carried out.  

The compounds described in the literature can be used as catalysts be used in the amounts specified there. Preferred Catalysts are, for example, nitrogen-containing compounds. Be particularly preferred exemplary catalysts are imidazole or Dimethylaminopyridine.

In a preferred embodiment of the method according to the invention rens the molar ratio of diol: trialkylsilyl halide, ins special trimethylsilyl chloride to a ratio between 1:10 and 5: 1, preferably between 1: 5 and 2: 1 and particularly preferably set a molar ratio between 1: 2 and 1: 3 and simultaneously a molar ratio of diol: base, especially triethylamine between 2: 1 and 1:20, preferably between 1: 1 and 1:15, particularly preferably chosen between 1: 2 and 1:10.

Another preferred embodiment of the Ver driving consists in the acetalization of a bis-silyl ether with 1,3-bis (benzyloxy) -2-formylpropane or its derivatives, reduction of the ent bis-benzyl ether to the diol, silylation of the diol to the bis Silyl ether and condensation of this bis-silyl ether with an aldehyde to the oligo-1,3-dioxane derivative. The one occurring in the reaction sequence Reduction of the bis-benzyl ether is known per se. Make benzyl ether important protective groups for alcohols. Their synthesis and their There is division in the literature (see e.g. T. W. Greene, P. G. M. Wuts, Protective Groups in Organic Synthesis, 2nd ed., John Wiley & Sons, Inc., New York, 1991, pp. 47-58 and the literature cited there) in detail described. Suitable embodiments of the reduction of benzyl ethers can be found, for example, in these references.

The bis-benzyl ether is preferably reduced on one suitable heterogeneous metallic catalyst with molecular Hydrogen as a reducing agent given the bis-benzyl ether if diluted in a solvent and with thorough mixing depending on the catalyst at temperatures from -20 ° C to 300 ° C, preferably  wise at temperatures from room temperature to 200 ° C, especially preferably at room temperature and at normal pressure or elevated Pressure, but preferably hydrogenated at normal pressure.

Metals such as palladium, platinum, rhodium or nickel are preferred used in the reduction of bis-benzyl ether. These metals can for example as a sponge like Raney nickel or in finely divided Form on a support such as aluminum oxide, silicon dioxide, Zeolites, activated carbon and. a. available. Particularly preferred catalyst systems are Raney nickel and palladium on activated carbon.

The choice of solvent is not critical. Suitable solvents are z. B. aliphatic or aromatic hydrocarbons, given if halogenated hydrocarbons such as hexane, heptane, cyclohexane, Benzene, toluene, dichloromethane, ethers such as diethyl ether, tetrahydrofuran, Alcohols such as methanol, ethanol, dioxane or mixtures of these solutions medium. Preferred solvent for the reduction of bis-benzyl ether are alcohols and ethers, particularly preferred are ethanol and Tetrahydrofuran.

In a particularly preferred embodiment, 1 part by weight of the Bis-benzyl ether in about 10 to 20 parts by weight of an inert solution by means of, in particular tetrahydrofuran, dissolved and with 0.1 part by weight a palladium catalyst, especially Pd / C (5%), added and at Room temperature hydrogenated without pressure until no more hydrogen is absorbed men will.

The compounds available via the new process as well Compounds according to the invention can, for. B. Make as follows:  

Scheme 1

Scheme 2

Scheme 3

Preferred compounds of the formula I * are prepared as follows:

Scheme 4

Scheme 5

The liquid-crystalline media according to the invention preferably contain as well as one or more compounds according to the invention as further components 2 to 40, in particular 4 to 30 components. These media very particularly preferably contain one or several compounds according to the invention 7 to 25 components. These further components are preferably selected from nematic or nematogenic (monotropic or isotropic) substance zen, in particular substances from the classes of azoxybenzenes, Benzylidenanilines, biphenyls, terphenyls, phenyl- or cyclohexyl benzoates, cyclohexane carboxylic acid phenyl or cyclohexyl esters, Phenyl or cyclohexyl ester of cyclohexylbenzoic acid, phenyl or Cyclohexyl ester of cyclohexylcyclohexane carboxylic acid, cyclohexyl phenyl ester of benzoic acid, cyclohexane carboxylic acid, or Cyclohexylcyclohexane carboxylic acid, phenylcyclohexane, cyclohexyl biphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, Cyclohexylcyclohexylcyclohexane, 1,4-bis-cyclohexylbenzenes, 4,4'-bis- cyclohexylbiphenyls, phenyl or cyclohexyl pyrimidines, phenyl or Cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or Cyclohexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenyl-cyclohexyl) - ethane, 1-cyclohexyl-2-biphenylylethane, 1-phenyl-2-cyclohexyl phenylethanes, optionally halogenated stilbenes, benzylphenyl ether, tolanes and substituted cinnamic acids. The 1,4-phenylene groups in these compounds can also be fluorinated.

The most important compounds which are suitable as further constituents of media according to the invention can be characterized by the formulas 1, 2, 3, 4 and 5:

R'-AE-R '' 1

R'-A-COO-E-R '' 2

R'-A-OOC-E-R '' 3

R'-A-CH ₂ CH ₂ -E-R "4

R ¹ -AC∼CE-R '' 5

In formulas 1, 2, 3, 4 and 5, A and E mean the same or ver can be different, each independently a bivalent Balance from the from -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr- -Dio-, -G-Phe- and -G-Cyc- as well as their mirror images formed group, where Phe is 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 Mean 2,5-diyl.

One of the radicals A and E is preferably Cyc, Phe or Pyr. E is in front preferably Cyc, Phe or Phe-Cyc. Preferably contain the inventions media according to the invention selected one or more components the compounds of formulas 1, 2, 3, 4 and 5, wherein A and E are selected are from the group Cyc, Phe and Pyr and simultaneously one or more Components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein one of the radicals A and E is selected from the group Cyc, Phe and Pyr and the rest of the rest 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 A and E are selected from the group -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.

R 'and R' 'in a smaller subset of the compounds of the Formulas 1, 2, 3, 4 and 5 each independently of the other alkyl, alkenyl, Alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy with up to 8 carbon atoms. This smaller subgroup is called Group A below and the compounds are represented by sub-formulas 1a, 2a, 3a, 4a and 5a designated. For most of these compounds, R 'and R' 'are from different from one another, one of these residues mostly alkyl, alkenyl, Is alkoxy or alkoxyalkyl.  

In another smaller subgroup, referred to as group B, of the compounds of the formulas 1, 2, 3, 4 and 5, R '' is -F, -Cl, -NCS or - (O) _i CH _{3- (k + l)} F _k Cl _l , where i is 0 or 1 and k + l is 1, 2 or 3; the connec tions in which R '' has this meaning are designated by the sub-formulas 1b, 2b, 3b, 4b and 5b. Those compounds of the sub-formulas 1b, 2b, 3b, 4b and 5b in which R ″ has the meaning -F, -Cl, -NCS, -CF ₃ , -OCHF ₂ or -OCF ₃ are particularly preferred.

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

In a further smaller subgroup of the compounds of the formulas 1, 2, 3, 4 and 5 means R '' - CN; this subgroup is hereinafter referred to as Group C designated and the compounds of this subgroup described accordingly with sub-formulas 1c, 2c, 3c, 4c and 5c. In the Compounds of the sub-formulas 1c, 2c, 3c, 4c and 5c have R 'those in the Compounds of 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 of the proposed substituents in use. All of these substances are obtainable according to methods known from the literature or in analogy.

In addition to compounds of the formula I according to the invention, the media according to the invention preferably contain one or more compounds which are selected from group A and / or group B and / or group C. The mass fractions of the compounds from these groups in the media according to the invention are preferred
Group A: 0 to 90%, preferably 10 to 90%, in particular 30 to 90%
Group B: 0 to 80%, preferably 10 to 80%, in particular 10 to 65%
Group C: 0 to 80%, preferably 5 to 80%, in particular 5 to 50%
wherein the sum of the mass fractions of the compounds from groups A and / or B and / or C contained in the respective media according to the invention is preferably 5 to 90% and in particular 10 to 90%.

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

The media according to the invention are produced in a manner which is customary per se Wise. As a rule, the components are dissolved into one another, for this purpose moderate at elevated temperature. With suitable additives, the liquid crystalline phases are modified according to the invention so that it in all types of liquid crystal display that have become known elements can be used. Such additives are the subject known and extensively described in the literature (H. Kelker / R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes can be used to produce colored ones Guest host systems or substances for changing the dielectric Anisotropy, the viscosity and / or the 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, the transformation into chemical formulas taking place according to the following tables A and B. All residues C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl residues with n or m C atoms. The coding according to Table B goes without saying. In Table A only the acronym for the basic body is given. In individual cases, a code for the substituents R ¹ , R ² , L ¹ and L ² follows with a dash, separately from the acronym for the base body:

Table A

Table B

The following examples are intended to illustrate the invention without limiting it. Percentages above and below mean percentages by weight. All temperatures are given in degrees Celsius. Sdp. Means boiling point, Mp. = Melting point, Kp. = Clearing point. Furthermore, K = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represent the transition temperatures. An means optical anisotropy (589 nm, 20 ° C.) and the viscosity (mm ² / sec) was determined at 20 ° C.

"Customary work-up" means: water is optionally added, extracted with dichloromethane, diethyl ether, n-pentane or toluene, separated, the organic phase is dried, evaporated and the product is purified by distillation under reduced pressure or crystallization and / or chromatography. The following abbreviations are used:
NaH: sodium hydride
BnBr: benzyl bromide
ClSi (CH ₃ ) ₃ : chlorotrimethylsilane
THF: tetrahydrofuran
pTsOH: p-toluenesulfonic acid
LiAlH ₄ : lithium aluminum hydride
NEt ₃ : triethylamine
DMF: N, N-dimethylformamide
Pd-Cx%: weight percent palladium on activated carbon
Me ₃ SiOTf: trimethylsilyl trifluoromethanesulfonate
TMS: trimethylsilyl.

example 1

A mixture of 250 mmol ethoxymethylene diethylmalonate (i), 250 mmol ethylene glycol, 300 ml xylene and 1.0 g p-toluenesulfonic acid is heated to 140 ° C. until pure xylene is distilled off from the mixture. The work is then carried out as usual. After distillation under reduced pressure, 2 is obtained .

step 2

A mixture of 1 mol 2 and 350 ml THF is slowly added under inert gas to a refluxed suspension of 1.317 mol lithium aluminum hydride, 300 ml toluene and 800 ml THF. After stirring under reflux for 1 hour, the mixture is cooled to 25 ° C. and hydrolyzed with a mixture of 40 ml of water and 200 ml of THF. Then it is worked up as usual. After distillation under reduced pressure, 3 is obtained .

step 3

A mixture of 100 mmol of 3 and 100 ml of THF is added dropwise to a suspension of 280 mmol of NaH and 200 ml of THF. After heating to 40 ° C., 220 mmol of benzyl bromide are added dropwise, the mixture is heated to 65 ° C. for 15 h and, after cooling to 0 ° C., hydrolyzed with 800 ml of water. Then it is worked up as usual. Chromatography gives 4 .

Step 4

A mixture of 100 mmol 4 , 13.0 mol formic acid and 500 ml toluene is stirred at room temperature for 18 h. After the usual work-up, 5 is obtained .

The following compounds of the formula are analogous to Example 1

produced:

Example 2

99 mmol of 5 in 20 ml of CH ₂ Cl _{2 are} added dropwise at -70 ° C. under an inert gas to a mixture of 92 mmol of 6 , 180 ml of CH ₂ Cl ₂ and 9 mmol of trimethylsilyl trifluoromethanesulfonate. After stirring for 2 hours at -70 ° C., 112 mmol of pyridine are added dropwise, the mixture is warmed to room temperature, 100 ml of saturated NaHCO ₃ solution are added, the mixture is stirred for a further 0.25 h and worked up as usual. Chromatography gives 7 .

Example 3

A solution of 106 mmol 7 in 700 ml THF is hydrogenated at normal pressure and 20 ° C to a standstill on 5 g Pd-C-5%. After the usual work-up and recrystallization, 8 is obtained .

Example 4

35 mmol of chlorotrimethylsilane are added dropwise to a mixture of 14 mmol of 8 , 70 mmol of triethylamine and 100 ml of N, N-dimethylformamide with inert gas and stirring. After stirring for 2 hours at 80 ° C. and cooling to room temperature, 100 ml of n-pentane are added to the mixture. Then it is worked up as usual. You get 9 .

Example 5

44 mmol of trans-2-hexenal in 20 ml of CH ₂ Cl _{2 are} added dropwise at -75 ° C. under an inert gas to a mixture of 40 mmol of 9 , 100 ml of CH ₂ Cl ₂ and 3 mmol of trimethylsilyl trifluoromethanesulfonate. After stirring for 2 hours at -75 ° C., 50 mmol of pyridine are added dropwise, the mixture is warmed to 0 ° C., 100 ml of NaHCO ₃ solution are slowly added and the mixture is worked up in the customary manner. After recrystallization from THF, 10 is obtained ; K 227 _B (189) I.

Analogous to Example 5 above, the following compounds of the formula

produced:

Examples 6-41

Claims (12)

1. Oligo-1,3-dioxane derivatives of the general formula I
wherein
R ¹ and R ^{2 are} each independently
an unsubstituted, an alkyl or alkenyl radical with 1 to 12 carbon atoms which is simply substituted by CN or CF ₃ or an at least single halogen substitution, wherein one or more CH ₂ groups in these radicals are each independently -O-, -S-, -CO-, -CO-O-, -O-CO- or -O-CO-O- can be replaced so that heteroatoms are not directly linked,
R ² also F, Cl or CN,
A ¹ and A ² each independently

• a) trans-1,4-cyclohexylene radical, in which one or more non-adjacent CH ₂ groups can also be replaced by -O- and / or -S-,
• b) 1,4-cyclohexenylene radical,
• c) 1,4-phenylene radical, in which one or two CH groups can also be replaced by N,
• d) radical from the group 1,4-bicyclo (2,2,2) octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, deca hydronaphthalene-2,6-diyl and 1,2, 3,4-tetrahydro naphthalene-2,6-diyl,

where the residues a), b) and c) can be substituted by CN or F,
Z ¹ and Z ² each independently
-CO-O-, -O-CO-, -CH ₂ O-, -OCH ₂ -, -CH ₂ CH ₂ -, -CH = CH-, -C∼C- or a single bond, and
m and n each independently
0 or 1,
where m + n = 0 or 1,
mean,
with the proviso that
when A ^{2 is} 1,4-cyclohexylene, n 1 and R ²
is in which one of the radicals X and Y is H, F or Cl and the other is F or Cl, Z ² -COO-, -OCO-, -CH ₂ O-, -OCH ₂ -, -CH ₂ CH ₂ -, - CH = CH- or -C∼C- is. 2. oligo-1,3-dioxane derivatives of the formula I according to claim 1, characterized characterized in that m and n are 0.   3. oligo-1,3-dioxane derivatives of the formula I according to one of claims 1 or 2, characterized in that R ¹ and R ² each independently of one another unsubstituted straight-chain alkyl, 1E- or 3E-alkenyl with 1 to 12 C- Mean atoms. 4. Oligo-1,3-dioxane derivatives of the formula
wherein
q and q 'are each independently 1 to 7
mean. 5. Oligo-1,3-dioxane derivatives of the formula
wherein
q 1 to 7, and
r '0 to 8
mean. 6. Oligo-1,3-dioxane derivatives of the formula
wherein
q 1 to 7, and
s' 0 to 6
mean. 7. Process for the preparation of oligo-1,3-dioxane derivatives of the general formula I *
wherein
R ¹ , R ² , A ¹ , A ² , Z ¹ and Z ^{2 have} the meaning given in claim 1,
m * and n * are each independently 0, 1 or 2, and
p * 1 or 2,
where m * + n * + p * = 2, 3 or 4,
mean,
with the provisos that

• (a) when p * 2, A ² 1,4-cyclohexylene, n * 1 and R ²
  is in which one of the radicals X and Y is H, F or Cl and the other is F or Cl, Z ² -COO-, -OCO-, -CH ₂ O-, -OCH ₂ -, -CH ₂ CH ₂ -, - CH = CH- or -C∼C-,
  and
• (b) when R ²
  where X ¹ and X ² each independently represent H, F or Cl, p * 2,

characterized in that a bis-silyl ether of the general formula II *
wherein
R ^a , R ^b and R ^{c are} each independently an alkyl radical having 1 to 6 carbon atoms or an aryl radical
mean,
condensed with an aldehyde of the formula OHC- (Z ² -A ² ) _{n *} -R ² . 8. Bis-silyl ether of the general formula II **
wherein
R ¹ , A ¹ and Z ^{1 have} the meaning given in claim 1,
m ** 0 or 1, and
R ^a , R ^b and R ^{c are} each independently an alkyl radical having 1 to 6 carbon atoms or an aryl radical
mean. 9. Aldehydes of the formula
wherein
Bn is a benzyl group in which the phenyl ring can also be substituted by alkyl, alkoxy, halogen, CN, NO ₂ or NH ₂ ,
means. 10. Liquid crystalline medium with at least two liquid crystalline Components, characterized in that there is at least one Contains oligo-1,3-dioxane derivative according to claim 1. 11. Liquid crystal display element, characterized in that it is a contains liquid-crystalline medium according to claim 10. 12. Electro-optical display element, characterized in that it as a dielectric, a liquid-crystalline medium according to claim 10 contains.