Arylpiperazines of the formula R-A-Z wherein R is ##SPC1## Or R.sub.2 --Q--, in which R.sub.1 is H, alkyl, Ar or COR.sub.3 ; R.sub.2 is H or alkyl; R.sub.3 is alkyl, aralkyl or substituted or unsubstituted aryl, and Q is --CX.sub.1 =CH--CO--, --C.tbd.C--CO--, --CH=CX.sub.1 --CO--, --CHX.sub.1 --CHX.sub.1 --CO--, --CO--CH=CX.sub.1 --, --CO--C.tbd.C--, --CO--CX.sub.1 =CH-- or --CO--CHX.sub.1 --CHX.sub.1 ; X.sub.1 is a functional group; A is C.sub.n H.sub.2n in which n is 1-4; Z is ##EQU1## AND Ar ...

D-(+)-Biotin can be prepared from optically active hydantoins of the formula I ##STR1## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given in patent claim 1, in a simple, stereospecific manner. Furthermore bicyclic nitriles of the formula XI ##STR2## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given represent precious intermediate products and educts of a multitude of possibilities to synthesize optically active D-(+)-biotin.

Enantiomers of optically active dicarboxylic acid monoesters are obtained by subjecting them to intramolecular rearrangement involving reversal of the direction of rotation.

The invention relates to an electrooptical liquid crystal display comprising a reorientation layer for reorientation of the liquid crystals. The field of said reorientation layer has a component parallel to the liquid crystal layer, said component being crucial for the reorientation. Said component comprises a liquid-crystalline medium having a positive dielectric anisotropy and contains at least one mesogenic compound of the formula (I), wherein R.sup.1 and L are delined as in claim 1.

D-(+)-Biotin can be prepared from optically active hydantoins of the formula I ##STR1## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given in patent claim 1, in a simple, stereospecific manner. Furthermore bicyclic nitriles of the formula XI ##STR2## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given represent precious intermediate products and educts of a multitude of possibilities to synthesize optically active D-(+)-biotin.

The invention relates to a process for preparing a support material having an increased number of reactive groups and to a process for preparing coreactive surfaces that may have catalytic or cocatalytic properties.

Optically active hydantoins of the formula I ##STR1## wherein X, Y, R.sup.1, R.sup.2 and R.sup.3 have the meaning given in Patent claim 1, are useful intermediate products for the preparation of D-(+)-biotin.

D-(+)-biotin can be prepared from optically active hydantoins of the formula I ##STR1## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given in Patent claim 1, in a simple, stereospecific manner. Furthermore bicyclic nitriles of the formula XI ##STR2## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given represent precious intermediate products and educts of a multitude of possibilities to synthesize optically active D-(+)-biotin.

D-(+)-biotin can be prepared from optically active hydantoins of the formula I ##STR1## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given in Patent Claim 1, in a simple, sterospecific manner. Furthermore bicyclic nitriles of the formula XI ##STR2## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given represent precious intermediate products and educts of a multitude of possibilities to synthesize optically active D-(+)-biotin.

D-(+)-Biotin can be prepared from optically active hydantoins of the formula I ##STR1## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given in patent claim 1, in a simple, stereospecific manner. Furthermore bicyclic nitriles of the formula XI ##STR2## wherein R.sup.1, R.sup.2, R.sup.3, X and Y have the meaning given represent precious intermediate products and educts of a multitude of possibilities to synthesize optically active D-(+)-biotin.