Asymmetric microbial reduction of tetralones

Abstract

The reduction of α- and β-tetralones [3,4-dihydronaphthalen-2(1H)-ones] and of 4-substituted-α-tetralones with Sporobolomyces pararoseus and Rhodotorula rubra is described. Both strains were grown in well aerated fermentors, in some cases improving the conversion yields up to 100%, and modifying the known selectivity of the reductions performed with S. pararoseus. All the reductions performed with R. rubra are enantioselective giving rise to (S)-alcohols, but they are weakly influenced by substituents at the 4-position. With this strain (S)-β-tetralol could be obtained with 90% ee and 100% conversion yield. Reductions performed with S. pararoseus are not enantioselective giving rise to (S)-and (R)-alcohols indicating the possible action of two reductases. These two reductases are strongly influenced by substituents at the 4-position, allowing only anti entry of the hydride, giving rise to cis-alcohols. cis-(1 R,4R)-4-Methyl-4-phenyl-1,2,3,4-tetrahydro-1-naphthol 12 could be obtained enantiomerically pure with an excellent conversion yield. The crystal structure of the Mosher ester derivative of compound 12 is described.