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Photoinduced Vinylcyclopropane-Cyclopentene Rearrangement: A Methodology for Chiral Bicyclo(3.2.0)heptenes. Formal Syntheses of (.+-.)-Grandisol and Naturally Occurring (-)-δ9(12)-Capnellene and Its Antipode.-Photosensitized irradiation of δ2-carene derivatives of type (I) (8 examples including (VIII)) efficiently and conveniently gives chiral bicyclo(3.2.0)heptenes (cf. (II), (III), (IX)). The utility of this photoinduced rearrangement is demonstrated in the formal syntheses of both the enantiomers of the marine natural product δ 9,12-capnellene (VII) and the sex pheromone (±)-grandisol (XII). The corresponding starting bicycloheptene isomers (IIIa) or (IIa) in the synthesis of the capnellene enantiomers are isolated in pure form after flash vacuum pyrolysis (ring-cleavage of (IIa)) or HPLC of the hydrolyzed (IIc)/(IIIc)-mixture, respectively. -(SONAWANE, H. R.; NAIK, V. G.; BELLUR, N. S.; SHAH, V. G.; PUROHIT, P. C.; KUMAR, M. U.; KULKARNI, D. G.; AHUJA, J. R.; Tetrahedron 47 (1991) 38, 8259-8276; Natl. Chem. Lab., Pune 411 008, India; EN)