FACILE ONE-POT THERMAL DEHYDRATION AND DETHIOACETALIZATION OF BETA-HYDROXYDITHIOACETALS WITH DIMETHYL-SULFOXIDE - SYNTHESIS OF ALPHA,BETA-UNSATURATED ALDEHYDES

The acyclic and cyclic beta-hydroxydithioacetals 3a-m and 4a-b obtaine d by sodium borohydride reduction (or Grignard addition) of the corres ponding beta-oxodithioacetals 2a-m are shown to undergo facile one pot thermal dehydration and dethioacetalization in the presence of dimeth yl sulphoxide to afford the corresponding ene- and polyene aldehydes 5 a-m and 6a-b in good yields. The probable mechanism of dethioacetaliza tion with dimethyl sulphoxide has also been discussed.