PHOTOCHEMICAL OXA-DI-PI-METHANE REARRANGEMENT APPROACH TO [3.3.3]PROPELLANES - TOTAL SYNTHESIS OF SESQUITERPENE HYDROCARBON (+/-)-MODHEPHENE

A photochemical approach to the construction of the [3.3.3]propellane and tricyclo[5.3.1.0(4,11]undecane ring systems through a common strategy employing oxa-di-pi-methane rearrangement as the key step is delineated. Starting from the readily available bicyclo[4.3.0]nona-1 (6),2-diene 6, the tricyclo[5.2.2.0(1,5)]undecenones 5 and 12 were prepared through a Diels-Alder strategy employing alpha-chloroacrylonitrile as the ketene equivalent. Sensitised irradiation of enone 5 furnished the tetra-cyclo[4.3.2.0(2,6).0(2,9]undecanone 4, which on regioselective, reductive C-C bond cleavage provided access to [3.3.3]propellanone 14. The tricyclic ketone 12 through a similar protocol furnished the tricyclo[5.3.1.0(4,11)]undecanone 16. The tetracyclic ketone 4 has been further elaborated in a straight-forward manner to afford the sesquiterpene hydrocarbon (+/-)-modhephene.