N-Acyliminium ion chemistry and palladium catalysis: a useful combination to obtain bicyclic heterocycles

By using N-acyliminium ion chemistry, several ω-propadienyllactams and a propadienyloxazolidine were prepared from N-acyliminium ion precursors and propargylsilanes. Treatment of these allene containing lactams and oxazolidinone with allyl halides or an allyl carbonate using Pd(II)-salts as the catalyst gave rise to a coupling–cyclization reaction, yielding bicyclic systems in which the allyl moiety is incorporated. With this methodology several substituted pyrrolizinones, an oxazolone and indolizinone were prepared.