A base-controlled regioselective synthesis of allyl and vinyl phenyl sulfones

A reaction of diethyl phenylsulfonylmethylphosphonate with 2-arylacetaldehydes in the presence of a catalytic excess of sodium hydride (1.1 equiv) yields allyl phenyl sulfones in excellent yield under mild reaction conditions. In contrast, when less than 1 equiv of sodium hydride (0.90 equiv) is used, the corresponding vinyl phenyl sulfones are obtained exclusively. The vinyl phenyl sulfones can be completely converted to allyl phenyl sulfones with only 0.2 equiv of NaH, suggesting that the second hydride involvement in the above transformation is catalytic. The regioselective control observed in these reactions offers a general method for synthesizing novel vinyl and allyl phenyl sulfones in one step from the same starting materials. The regioselectivity and stereoselectivity of this reaction, however, are not maintained when 2-alkylacetaldehydes are reacted with diethyl phenylsulfonylmethylphosphonate under identical reaction conditions. Our results indicate that an extended conjugation of the double bond in allylsulfones formed from the reaction of 2-arylacetaldehydes is required for the observed regio- and stereoselectivity.