Structural diversity through intramolecular cycloaddition and modulation of chemical reactivity in excited state. Synthesis and photoreactions of 3-oxa-tricyclo[5.2.2.01,5]undecenones: novel stereoselective route to oxa-triquinanes and oxa-sterpuranes

Synthesis of 11-methyl-3-oxa-tricyclo[5.2.2.01,5]undecenones by intramolecular Diels–Alder reaction of highly labile spiroepoxycyclohexa-2,4-dienones and its photochemical reactions upon triplet (3T) and singlet (1S) excitation leading to a stereoselective route to oxa-triquinane and oxa-sterpurane, respectively, is described.