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

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