Homochiral (R)- and (S)-1-heteroaryl- and 1-aryl-2-propanols via microbial redox

Preparation of various heteroaryl propanols 2a-g and of the corresponding propanones 3a-g as starting materials for microbial redox is described. The kinetic resolution of the racemic propanols 2a-g is obtained via oxidation with Pseudomonas paucimobilis and Bacillus stearothermophilus [(R)-alcohols, ee 74-100%]. Similar results are achieved with 3-(2-hydroxypropyl)trifluoromethylbenzene 7 (44%, ee 100% of the (R)-alcohol 6). The reduction of the propanones 3a-d and 3g with baker's yeast and other fungi gives the (S)-alcohols tee 100%). The pure (S)-alcohols are also obtained by reduction of 1-[3-(trifluoromethyl)phenyl]-2-propanone 7. 1-[(4,4-Dimethyl)-2-(Delta(2))oxazolinyl]-2-propanone 3e and 1[2-(Delta(2))-thiazolinyl)-2-propanone 3f are not reduced. The heterocyclic rings of (S)-5-(2-hydroxypropyl)-3-methylisoxazole 2d and of (S)-2-(2-hydroxypropyl)-4-methylthiazole 2g are deblocked to the homochiral enamino ketone: 8 (78%) and to the protected B-hydroxy aldehyde 9 (73%), respectively. The (R)-3-(2-hydroxypropyl)trifluoromethylbenzene 6 is transfomed into the homochiral precursor of (S)-fenfluramine 10 (overall yield 65%). (C) 1998 Elsevier Science Ltd. All rights reserved.