Optically active compounds

Details Optically active compounds Optically active compounds

2000-12-11

2003-08-19

Huff, Mark F. (Department: 1756)

Compositions

Liquid crystal compositions

C549S453000

Reexamination Certificate

active

06607677

ABSTRACT:

This invention relates to optically active materials and their use as doping agents for liquid crystals for a wide range of applications including solid state cholesteric filters for projection displays, circular polariser, optical filter, etc.
The addition of an optically-active compound to a non-optically-active liquid crystalline phase is one of procedures used for the conversion of non-optically-active into optically-active mesophases. The nematic phase, for example, is converted to the cholesteric one when being doped with a small amount of an optically-active substance. This conversion manifests itself by the occurrence of an intermolecular helix which is characterised by the so-called helical twisting power (HTP) given in Equation 1:
HTP
=
&LeftBracketingBar;
ⅆ
p
-
1
ⅆ
x
&RightBracketingBar;
x
=
0
≅
p
-
1
x
=
∑
i
⁢
x
i
⁡
(
HTP
)
,
(
1
)
Said HTP is in fact a measure for the efficiency of a given dopant and is determined by the Cano method with solutions of the dopant in the host mesophase. Since the optically-active guest and the non-optically-active host compounds are not necessarily compatible at the molecular scale, their binary solution is frequently characterised by undesirable changes of the thermo-tropic sequence of the initial host liquid crystalline material, like for example a depression of the clearing point. Those changes could in turn have negative effects on the phase properties of the host, such as a decrease of the birefringence etc. Therefore, an optically-active dopant is sought so that with very small concentrations of this latter, large values of HTP could be induced.
As such efficient optically-active dopants there are the binaphthol derivatives described in GB-A-2 298 202. However optically-active binaphthol derivatives may undergo partial racemisation when being heated. Besides, their preparation is expensive because it includes asymmetric resolution of binaphthol racemate as a crucial reaction step.
Another type of optically-active dopants are the TADDOLs derivatives (&agr;,&agr;,&agr;′,&agr;′-tetraaryl-1,3-dioxolane-4,5-dimethanols). They have been known for 15 years in asymmetric syntheses (D. Seebach et al.,
J. Org. Chem.
60, 1788, (1995) and
Helv. Chim. Acta
80, 2515, (1997)) and recently investigated as dopants in nematic host mesophases and found to induce large values of HTP (H. G. Kuball et al.,
Helv. Chim. Acta
80, 2507, (1997) and International Patent Application WO-A-97/34886). This efficiency of TADDOLs compounds was essentially attributed to their conformational stability due to the presence of the dioxolane ring.
Tet. Lett.
36(11), 1995, 1827-1830 (Dube et al.) discloses the compound (2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol as an intermediate in asymmetric synthesis:
However, no activity is given for the compound.
EP-A-0233602 (Hoechst AG) relates to chiral dopants for liquid crystals. The compounds are all derivatives of butane-1,2,3,4-tetraol of general formula:
having no further substituents on the butane backbone.
It has been suggested that the large HTP observed with TADDOLs compounds is due to their conformational stability. However we have now discovered that further compounds that exhibit overcrowding of the chiral atoms and are sterically hindered at positions analogous to the &agr;,&agr;′ positions in TADDOLs are equally effective at producing a large HTP.
Thus the invention provides optically active butane-1,2,3,4-tetraol derivatives of formula I:
in which
A
1
, A
2
, A
3
, A
4
each independently represents hydrogen; or an optionally-substituted methyl group; or an optionally-substituted aliphatic group with 2 to 80 C-atoms, in which one or more C-atoms may be replaced by a heteroatom or a group —SO—, —SO
2
—, —SOO—, —OSO— or —SOS—; or an optionally-substituted aromatic or non-aromatic carbocyclic or heterocyclic ring system, with 1 to 80 C-atoms; and
A
5
, A
6
, A
7
, A
8
each independently represents an optionally-substituted aliphatic group with 3 to 80 C-atoms, in which a C-atom, or two or more non-adjacent C-atoms, may be replaced by a heteroatom or a group —SO—, —SO
2
—, —SOO—, —OSO— or —SOS—; or an optionally-substituted aromatic or non-aromatic carbocyclic or heterocyclic ring system, with 1 to 80 C-atoms; or
one, two or three of A
5
, A
6
, A
7
and A
8
independently represents hydrogen; or an optionally-substituted methyl group; or an optionally-substituted aliphatic group with 2 C-atoms, in which a C-atom may be replaced by a heteroatom; and the remainder of A
5
, A
6
, A
7
, A
8
independently represent an optionally-substituted aliphatic group with 3 to 80 C-atoms, in which a C-atom, or two or more non-adjacent C-atoms, may be replaced by a heteroatom, or a group —SO—, —SO
2
—, —SOO—, —OSO— or —SOS—; or an optionally-substituted aromatic or non-aromatic carbocyclic or heterocyclic ring system, with 1 to 80 C-atoms;
with the provisos that:
when one, two or three of A
5
, A
6
, A
7
and A
8
represents hydrogen, then A
5
, A
6
, A
7
and A
8
may not represent COOH; and
when A
5
, A
6
, A
7
and A
8
are all phenyl, then at least one of A
1
, A
2
, A
3
, A
4
does not represent hydrogen.
The term “aliphatic” includes straight-chain and branched alkyl, as well as saturated and unsaturated groups. Possible substituents include alkyl, aryl (thus giving an araliphatic group) and cycloalkyl, as well as amino, cyano, epoxy, halogen, hydroxy, nitro, oxo etc. Possible heteroatoms which may replace carbon atoms include nitrogen, oxygen and sulphur. In the case of nitrogen further substitution is possible with groups such as alkyl, aryl and cycloalkyl.
In the case of the present invention, owing to the absence of the dioxolane ring, the new optically active butane-1,2,3,4-tetraol derivatives of formula I have obviously more conformational freedom then TADDOLs derivatives. However they were surprisingly found still to induce large values of HTP when being used as dopants in nematic host systems, as will be demonstrated in the forthcoming sections.
The compounds of the invention may be used as doping agents for liquid crystals for a wide range of applications including solid state cholesteric filters for projection displays, circular polarisers, optical filters, etc.
Although one or more of A
5
, A
6
, A
7
and A
8
may represent a small group such as hydrogen or an optionally-substituted methyl group, we prefer there to be two bulkier groups, A
5
and A
6
, attached to the same carbon atom. Thus preferably only A
7
and A
8
may represent hydrogen. More preferably only one of A
5
, A
6
, A
7
and A
8
may represent hydrogen. The best compounds are those which have four bulky groups. Thus, preferably A
5
, A
6
, A
7
and A
8
each independently represents an optionally-substituted aliphatic group with 3 to 80 C-atoms, in which a C-atom, or two or more non-adjacent C-atoms, may be replaced by a heteroatom or a group —SO—, —SO
2
—, —SOO—, —OSO— or —SOS—; or an optionally-substituted aromatic or non-aromatic carbocyclic or heterocyclic ring system, with 1 to 80 C-atoms. Carbocyclic or heterocyclic ring system having two or more fused rings have been found to be particularly suitable.
The invention further relates to optically active butane-1,2,3,4-tetraol derivatives of formula I, in which:
A
1
, A
2
, A
3
, A
4
each independently represents hydrogen; or an optionally-substituted methyl group; or an optionally-substituted aliphatic group with 2 to 80 C-atoms, in which one or more C-atoms may be replaced by a heteroatom or a group —SO—, —SO
2
—, —SOO—, —OSO— or —SOS—; or an optionally-substituted aromatic ring system, with 1 to 80 C-atoms; and
A
5
, A
6
, A
7
, A
8
each independently represents an optionally-substituted aliphatic group with 3 to 80 C-atoms, in which a C-atom, or two or more non-adjacent C-atoms, may be replaced by a heteroatom or a group —SO—, —SO
2
—, —SOO—, —OSO— or —SOS—; or an optionally-substituted aromatic ring system, with 1 to 80 C-atoms;
with the proviso that, when A
5
, A
6
, A
7
and A
8
are all phenyl, then at least one of

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