Lewis acid mediated reactions of N-arylsulfonimidoyl chlorides with alkenes.: Some steric effects of alkene substitution

The Lewis acid-mediated reaction of N-phenyl-S-(4-methylphenyl)sulfonimidoyl chloride with alkenes was explored in order to determine the effect of alkene substitution on the stereochemical outcome of the reaction. With monosubstituted alkenes, benzothiazines are produced with relatively low diastereoselection, with one unique exception, trimethylsilylethene. 1,1-Disubstituted alkenes give products with even lower stereoselectivity. With trisubstituted alkenes, steric effects begin to change the course the reaction from one which can be rationalized as a cycloaddition to one which seems to definitely produce a carbocationic intermediate. Interestingly, the stereoselection observed in the reaction of (E)- and (Z)-2-butenes shows large deviations from the norm with (E)-2-butene giving rise to two diastereomeric benzothiazines in a ratio of 45:1.