Photoinduced Vinylcyclopropane-Cyclopentene Rearrangement: A Methodology for Chiral Bicycloheptenes. Formal Syntheses of (+/-)-Grandisol and Naturally Occurring (-)-Δ9(12)-Capnellene and its Antipode

Article abstract of DOI:10.1016/S0040-4020(01)91019-1

The problem of achieving reaction selectivity in cis-alkyl vinylcyclopropanes in favour of their rearrangement to cyclopentenes, obviating the competing low energy process of the <1,5> (homo)sigmatropic hydrogen shift, is addressed.It has been demonstrated that the readily available bicyclo<4.1.0>heptenes derived from (+)-Δ³-carene (1), upon photosensitized irradiation, are conveniently transformed into chiral cis-bicyclo<3.2.0> heptenes.The synthetic potential of this strategy has been demonstrated in realization of efficient formal syntheses of the important insect sex pheromone (+/-)-grandisol (2) and both the enantiomers of Δ⁹⁽¹²⁾-capnellene (3) from readily available 1, a major component of Indian turpentine oil.