Dipolar cycloaddition of an intermediary N-acyltrimethylsilylmethyliminium salt formed from N-(benzylidene) trimethylsilylmethylamine and acyl chloride to conjugated alkenes or alkines gave N-acylpyrrolidines or N-acyl-2, 5-dihydropyrroles, respectively. The stereochemistry of all the products was established.
