Abstract The reactive 1, 3-dipoles ethoxycarbonylformonitrile oxide, benzonitrile oxide, diphenylnitrile imine and benzonitrilium 4-nitrobenzylid add to the 4-methylenecyclohexa-2, 5-dienone (1) to give the respective 1: 1 cycloadducts (4a-d). The yields are high and the reactions therefore provide ready access to members of the hetero-spiro [4, 5] decatrienone system. Diazomethane, phenyldiazomethane and diphenyldiazomethane also add to the ...