Diastereoselective addition reactions of racemic chiral vinyl sulfimides

S-Aryl S-vinyl sulfimides are prepared by a new method via Horner-Wadsworth-Emmons reagents generated in situ. Lewis acid-catalysed Diels-Alder reaction of S-ethenyl-S-phenyl-N-tosylsulfimide with cyclopentadiene leads to the endo anti product with good diastereofacial and endo-exo selectivities. A range of alcohols and amines, with the limitation that they be practically usable in large excess, add to β-aryl vinyl sulfimides with modest diastereoselectivity. The major products of both the cycloaddition and the nucleophilic additions are rationalised by a model invoking addition to the least-hindered face of the s-cis conformation of the vinyl sulfimide.