Synthesis and photoreactions of 3-oxa-tricyclo[5.2.2.01,5]undecenones: a novel, stereoselective route to oxa-triquinanes and oxa-sterpuranes

The synthesis of 11-methyl-3-oxa-tricyclo[5.2.2.01,5]undecenones and their photochemical reactions upon triplet (3T) and singlet (1S) excitation is described. Oxidation of hydroxymethylphenol gave a ketoepoxide by intramolecular cycloaddition. Manipulation of the oxirane ring furnished the chromophoric systems. Triplet excitation of these gave tetracyclic compounds containing an oxatriquinane framework. Singlet excitation furnished the tricyclic compound having an oxasterpurane ring system in a stereoselective fashion.