Synthesis and Dienophilic Behavior of Enantiomerically Pure (Z)-3-p-Tolylsulfinylacrylonitriles

Abstract

The syntheses of enantiomerically pure (Z)-3-p-tolylsulfinylacrylonitrile (1b) and its 2-n-butyl (1a), 2-tert-butyl (1c), and 2-benzyl (1d) derivatives, by stereoselective hydrocyanation with Et 2 AlCN of their corresponding alkynylsulfoxides, are described. Asymmetric Diels-Alder reactions of these dienophiles with cyclopentadiene are also reported, the most significant finding being their total π-facial diastereoselectivity, controlled by the sulfur configuration, which can be readily inverted by using BF 3 as a catalyst. The endo selectivity is very high for 1b under thermal and catalytic (ZnBr 2 ) conditions and complete in the presence of BF 3 , whereas 1a and 1d only exhibit a complete endo selectivity in the presence of BF 3 .