Studies on cycloaddition of spiroepoxycyclohexa-2,4-dienones with indene and sigmatropic shifts in excited states: Synthesis of benzotricyclo[5.2.2.02,6]undec-10-en-9-ones,annulated polyquinanes and bicyclo[4.2.0]octanoids

A regio- and stereoselective cycloaddition of 6,6-spiroepoxycyclohexa-2,4-dienones with indene leading to benzo-annulated spiroepoxytricyclo5.2.2.0^2,6]undec-10-en-9-ones has been described. Manipulation of the oxirane ring in adducts furnished benzotricyclo5.2.2.0^2,6]undecanes endowed with a β,γ-enone chromophore. Photochemical reaction of β,γ-enones upon direct irradiation (1S) gave annulated bicyclo4.2.0]octenones as a consequence of a stereoselective 1,3-acyl shift. Triplet excitation of chromophoric systems led to oxa-di-π-methane reaction and gave pentacyclic products which upon cleavage of cyclopropane ring furnished benzoannulated triquinanes. An interesting effect of substituent on the photoreaction has also been observed.