The Preparation and Photoreaction of Spiro2,7>octen>-8'-ones. An Intramolecular Cycloaddition of Photochemically Generated Ketene with the Epoxide Ring

Article abstract of DOI:10.1246/bcsj.56.2009

The oxidations of 1,5-dimethyl- and 1,3,5-trimethyl-6-methylenetricyclo<3.2.1.0^2,7>oct-3-en-8-ones with 3-chloroperbenzoic acid or thallium(III) acetate resulted in the formation of 1',5'-dimethyl and 1',3',5'-trimethylspiro2,7>oct<3>en>-8'-ones (2a and 2b).The oxidation occured stereoselectively on the exocyclic double bond from the exo-side.The photochemical reactions of 2a and 2b resulted in the formation of 4,8-dimethyl and 4,6,8-trimethyl-3,4-dihydro-1H-2-benzopyran-3-ones, both of which would be derived from an ene-type reaction of the ketene intermediate with the epoxide ring involved in the <4? + 2?> electronic system.The intermediacy of the ketene was assessed by low-temperature infrared spectrosopy as well as by a trapping experiment, the mechanistic pathways were confirmed by conducting the photoreaction in deutereted methanol.