1,3-Dipolar cycloadditions of nitrile oxides with 4-carbethoxymethyleno-4,5,6,7-tetrahydro-6,6-dimethylbenzo[c][1,2,5]oxadiazole

The (E)- and (Z)-α,β-unsaturated esters, 3 and 4 are prepared by applying a Wittig reaction on the ketone 1. Stable nitrile oxides are added to the stable (E)-isomer 3 resulting to the formation of the spiro-derivatives 7 , whereas with the unstable nitrile oxides a second stereoisomer 8 is also formed. Mesitonitrile oxide reacts also with the ketone 1 to give the spiro-cycloadduct 10. The assignment of regio-isomers 7 was deduced from their spectral data as well as from some molecular orbital considerations.