Lewis acid mediated [3+2] and [3+3] annulations of azomethine imine with donor-acceptor cyclopropanes

Two different Lewis acids were used for developing [3+2] and [3+3] regioselective cycloaddition reactions of an azomethine imine with activated cyclopropanes. Scandium(III) triflate catalyzes a [3+2] cycloaddition reaction of the azomethine imine with cyclopropanes to form tetrahydropyrazolone derivatives and tricyclic tetrahydrofuran derivatives in moderate yields. Complementary to this, a novel [3+3] cycloaddition reaction of the azomethine imine with activated cyclopropanes was developed by using EtAlCl2 as a Lewis acid to form hexahydropyridazinone derivatives in high regioselectivity.