Reactions of Keteniminium Salts with Alkenes

Keteniminium salts, generated in situ from dialkylamides or a-haloenamines, are more reactive compared to ketenes and react with alkenes in a stepwise cycloaddition to give cyclobutanones. However, the cycloaddition is limited to mono- and 1,2-disubstituted alkenes. 

C2-Symmetric pyrrolidines have been employed as chiral auxiliaries effectively. Intramolecular cycloadditions of keteniminium salts as well as reactions with imines furnishing 3-lactams have been reported in the literature.  

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