Abstract: The invention relates to a method for the stereoselective preparation of a hetero-bicyclic alcohol enantiomer, characterized in that a substantially pure enantiomer of the general formula ##STR1## is prepared from a compound of the general formula ##STR2## wherein the variable are as defined as in claim 1. The method comprises the following successive reaction steps:(i) reaction with a substantially enantiomerically pure compound of the general formula ##STR3## wherein Z, R.sub.3 and R.sub.4 are defined as in claim 1; (ii) subjection of the compound formed to a deprotection/ring-closure reaction;(iii) optionally deprotection of the hydroxy group of the ring-closed product.The invention further relates to enantiomerically pure intermediates, the preparation of these intermediates and the preparation of a starting compound.

Abstract: The invention relates to an enzymatic process for the stereoselective preparation of a hetero-bicyclic alcohol enantiomer, characterized in that a substantially pure enantiomer of the general formula ##STR1## wherein X is O, S, NH, N--(C.sub.1 -C.sub.4)alkyl or CH.sub.2 ; Y.sub.1, Y.sub.2 and Y.sub.3 are each independently hydrogen or substituents selected from halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 haloalkyl, nitro and cyano;the NO.sub.2 substituent is attached to the bicyclic ring system in the 5- or 7-position; andthe C*-atom has either the R or the S configuration;is prepared from its corresponding alcohol racemate by the following successive reaction steps:(1) stereoselective esterification,(2) separation of the alcohol from the ester produced,(3) hydrolysis of the ester to produce the corresponding alcohol enantiomer, and(4) conversion of the alcohol enantiomer into the starting racemate under basic conditions in order to allow its reuse.