Intramolecular substitution reactions involving π-nucleophiles and N-acyliminium cations generated from azetidin-2-ones

The Lewis acid-catalyzed intramolecular substitution reactions of 4-vinyloxy- or 4-acyloxy-azetidin-2-ones with nitrogen-bound allyl-, propargyl- and vinyl-silanes leading to the carbacephams or carbacephems, are reported. The formation of carbapenams was not observed. To illustrate the potential of these reactions to be carried out under solid-phase conditions, a synthesis of diastereomeric 5-vinyl-carbacephams via the cyclization/cleavage methodology was performed.