Asymmetric oxidation of 1,3-dithianes to 1,3-dithiane 1-oxides

Abstract

Oxidation of 2-(1-hydroxy-1-methylethyl)-1,3-dithiane with the Sharpless reagent has been examined under various reaction conditions. Oxidation of 2-(1-hydroxy-1-methylethyl)-1,3-dithiane with Ti(OPrⁱ)₄–diethyl L-(+)-tartrate–tert-butyl hydroperoxide (1∶2∶1.5) in CH₂Cl₂ in the presence of 4 Å molecular sieves gives (1S,2S)-2-(1-hydroxy-1-methylethyl)-1,3-dithiane 1-oxide with high trans selectivity and with moderate enantioselectivity. The enantioselectivity depends upon the substituent at the 2-position of the 1,3-dithiane. Oxidation of 2-(1-methoxy-1-methylethyl)- and 2-(1-acetoxy-1-methylethyl)-1,3-dithiane gives (1S,2S)-2-(1-methoxy-1-methylethyl)- and (1R,2S)-2-(1-acetoxy-1-methylethyl)-1,3-dithiane 1-oxides, respectively in >99% ee.