The Preparation and Photoreation of Spiro[oxirane-2,6′-tricyclo[3.2.1.02,7]oct[3]en]-8′-ones. An Intramolecular Cycloaddition of Photochemically Generated Ketene with the Epoxide Ring

Abstract

Abstract The oxidations of 1,5-dimethyl- and 1,3,5-trimethyl-6-methylenetricyclo[3.2.1.02,7]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′-trimethylspiro[oxirane-2,6′-tricyclo[3.2.1.02,7]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 exoxide ring involved in the [4π+2σ] electronic system. The intermediacy of the ketene was assessed by low-temperature infrared spectroscopy as well as by a trapping experiment, the mechanistic pathways were confirmed by conducting the photoreaction in deuterated methanol.