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

Abstract 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.