Divergent selectivity in MgI2-mediated ring expansions of methylenecyclopropyl amides and imides

We report a novel approach to prepare five- and six-membered heterocyclic compounds via a ring expansion of monoactivated methylenecyclopropanes (MCPs) with aldimines and aldehydes in the presence of MgI2. Monoactivated MCPs behave as homo-Michael acceptors to afford bifunctional vinylogous enolates in the presence Of MgI2. The carbonyl moiety of the monoactivated MCP dramatically influences the reaction site in the dienolate with aryl aldimines and aldehydes as well as the size of the ring. Excellent divergent selectivity to five- vs. six-membered heterocycles is observed: alpha-alkylation/5-exo-tet cyclization (Z = NPh2) VS, gamma-alkylation/6-exo-trig cyclization (Z = 2-oxazolidone). Analogously, the reaction of the MCP imide with alkyl aldmines demonstrates the same selectivity by varing the size of electrophile or the reaction temperature. In addition, we observe the first example of the formation of the gamma-alkylation adduct in the reaction of a vinylogous imide enolate with a carbonyl compound.