Asymmetric synthesis of polysubstituted methylenecyclobutanes via catalytic [2+2] cycloaddition reactions of N-allenamides.

A highly enantioselective [2+2] cycloaddition reaction of alkylidene malonates with the internal C=C bond of N-allenamides was developed with a MgII/N,N′-dioxide complex as a catalyst. Various polysubstituted methylenecyclobutanes were afforded in good yields (up to 99%) and excellent enantioselectivities (up to 96% ee) under mild conditions. The utility of the donor–acceptor cyclobutane product was demonstrated as a masked 1,4-dipole in the formal [4+2] annulation reaction with a silyl enol ether. [ABSTRACT FROM AUTHOR]