PHOTOCYCLOADDITION OF 5,5-DIMETHYL-6-OXOCYCLOHEX-1-ENE-1-CARBONITRILETO ALKENES

While irradiation (350 nm) of the title cyanocyclohexenone 3a in the p resence of 2,3-dimethylbut-2-ene affords hexahydroindeno-1,2-oxazole 6 selectively, photolysis of 3a in the presence of 2-methylbut-2-ene or isobutene gives mixtures of tricyclic 1,2-oxazoles and 2-oxobicyclooc tane-1-carbonitriles, the product ratio oxazole/bicyclooctane decreasi ng with increasing I-p of the alkene. The constitution of the photopro ducts indicate that oxazoles and bicyclooctanes result from two isomer ic triplet 1,4-biradicals, formed by addition of the less substituted C-atom of the alkene to either of the olefinic C-atoms of triplet 3a, respectively. (C) 1998 Elsevier Science S.A.