Regio- and chemoselective conjugate 1,4-reduction of α-oxoketene dithioacetals with sodium borohydride and sodium cyanoborohydride

Theα-oxoketene dithioacetals 1 are shown to undergo conjugate 1,4-reduction in highly regio- and chemoselective manner with sodium borohydride in acetic acid to afford the corresponding β-oxodithioacetals 5 in good yields. These results have been rationalized according to HSAB principle in terms of 'hard soft affinity inversion' concept. The reduction of 1 with sodium cyanoborohydride also proceeds in 1,4-conjugate addition-elimination manner to afford the corresponding vinylogous thiolesters 6 in good yields.