1,3-Dipolar Cycloaddition Reactions Initiated with the 1,5-Dimethyl-3-phenyl-6-oxoverdazyl Radical

The 1,5-dimethyl-3-phenyl-6-oxoverdazyl radical reacts at room temperature in the presence of styrene to give a dihydrotetrazinone heterocyclic structure. We surmise that the reaction occurs by a 1,3-dipolar cycloaddition via the intermediacy of an azomethine imine. While initial reactions under nitrogen gave relatively poor yields (40 %) of the cycloaddition product, improved yields (up to 84 %) were realized when the reaction mixtures were saturated with oxygen. Acrylate, methacrylate, fumarate and maleate dipolarophiles react regioselectively and stereospecifically to provide a series of dihydrotetrazinone heterocyclic structures. These initial results demonstrate the feasibility of using verdazyl radicals as substrates for organic synthesis.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)