Synthesis of 1,3-dithianes and 1,3-dithiolanes. Baker's yeast reduction and lipase-catalyzed resolution for synthesis of enantiopure derivatives

Three 1,3-dithiolanes and four 1,3-dithianes have been synthesised from 1-( 1,3-dithiolan-2-yl)-2-propanone and 1-(1,3-dithian-2-yl)-2-propanone, respe ctively. Asymmetric reductions of these ketones using baker's yeast gave th e corresponding enantiopure (S)-alcohols. Baker's yeast also reduced the do uble bond in 3-(1,3-dithian-2-yl)-3-buten-2-one enantioselectively to give (S)-3-(1,3-dithian-2-yl)-2-butanone. 3-(1,3-Dithian-2-yl)-3-buten-2-one was also reduced chemoselectively and the resulting 3-(1,3-dithian-2-yl)-3-but en-2-ol was resolved by transesterification in organic solvent using lipase B from Candida antarctica to yield the (S)-alcohol and the (R)-acetate wit h very high enantiomeric ratio, E. Racemic 1-(1,3-dithiolan-2-yl)-2-propano l and 1-(1,3-dithian-2-yl)-2-propanol were also resolved under similar cond itions to give the (S)-alcohols and the corresponding (R)-acetates.