A new synthesis of 4-thiofuranosides via regioselective opening of an episulfide with allylmagnesium bromide

A new synthesis of 4-thiofuranosides which might be of general interest is described. (2R,3S)-3-[[(4-Bromobenzyl)oxy]methyl]oxirane-2-methanol (1) was converted to the corresponding epithio derivative 2 with inversion of configuration at both chiral centers. Regioselective opening of compound 2 with allylmagnesium bromide gave thiol 3a which was benzoylated. Oxidative cleavage of the olefinic bond, followed by ring closure and protective group exchange, gave the desired 4-thiofuranoside derivative 9