Thermally induced [2+2] cycloadditions of (Benzyloxymethylene)cyclopropane with alkylidenemalononitriles

The reaction of (benzyloxymethylene)cyclopropane (1a) with alkylidenemalononitriles 2 at ambient pressure afforded the corresponding cyclobutane derivatives 3 in good-to-high yields. For example, the reaction of 1a with benzylidenemalononitrile (2a), (2-naphthylmethylene)malononitrile (2e), and tert-butylmethylenemalononitrile (2f) in acetonitrile at 80 °C gave the corresponding cyclobutanes 3a, 3e, and 3f in 96, 96, and 91 % yield, respectively. Control experiments proved that the reaction proceeds via well-stabilized zwitterionic intermediate 6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)