N-Acyliminium ion cyclizations of trimethylsilylmethylallenes

N-Acyliminium ion cyclizations were studied with allenylmethylsilanes to synthesize nitrogen heterocycles. N-Acyliminium ion cyclizations were carried out by exposure of precursors 6 and 7 to Lewis acid. The precursors 6 were converted to pyrrolizidinone derivatives 9 with an exo-allene moiety, while the precursors 7 to indolizidinone derivatives 10 with an exo-1,3-diene moiety.