Synthesis of enantiomerically pure (1R,2R)- and (1S,2S)-2-alkyl-1-phenylsulfonylcyclopropanes using Bakers’ yeast

Abstract

Reduction of the ketone 1 with Bakers’ yeast gives the alcohol (R)-2 with high enantiomeric excess, and this upon subsequent epoxidation and alkylation with Grignard reagents provides the alcohols (S)-4 without racemisation. Tosylation of the alcohols (S)-4 under common conditions yields the tosylates (toluene-p-sulfonates) (S)-5, whilst under Mitsunobu conditions inversion of configuration takes place giving the tosylates (R)-5. Subsequent treatment of the tosylates (S)-5 and (R)-5 with lithium diisopropylamide leads to cyclization affording the enantiomerically pure cyclopropanes (S,S)-6 and (R,R)-6 in high yields, respectively. The diastereoisomeric alcohol (S)-4f, obtained by methylation of the alcohol (S)-4e, can also be converted into the single stereoisomer (R,R)-6f in enantiomerically pure form.