Domino Thermal Rearrangement/[4+2] Addition Reactions of an exo-Methylene Spirocyclopropane Isoxazolidine

A 4-methylene-5-spirocyclopropane isoxazolidine was prepared with complete regioselectivity through the 1,3-dipolar cycloaddition reaction of a pyrroline N-oxide with a cyclopropylidene acetate, followed by reduction and elimination. Thermal rearrangement of the isoxazolidine gives an indolizidinone that retains the exocyclic methylene moiety. The exo-methylene substituent confers a particular reactivity to this heterocycle; it can undergo thermal hetero-Diels-Alder cycloadditions and ene reactions with different reaction partners.