1,3-Dipolar cycloadditions of heterocycles 1. Cycloadditions ofC-benzoyl-N-phenylnitrone to furan

A frontier orbital treatment of furan suggests its possible reactivity in 1,3-dipolar cycloadditions with dipoles posessing low lying LUMO's, such as nitrones, especially those with electronwithdrawing substituents. By the reaction ofC-benzoyl-N-phenylnitrone1a with an excess of furan at 60° the monocycloadduct2a, two biscycloadducts4 and5 and further reaction products of nitrone such as azoxybenzene8, diketoamide9a, benzoanilide10a, benzoic acid11a and phenyl glyoxylic acid12 were isolated. The cycloaddition ofC-(4-bromobenzoyl)-N-phenylnitrone1b with furan is also reported.