Labda-7,14-dien synthesis

The photosensitized oxygenation of 12(Z)-abienol has been studied in a biomimetic synthesis of tobacco labdanoids. In the reaction with singlet oxygen the major process is an ene-reaction involving attack at C-13 and yielding after reduction the 11(H),13(/ and 5)-labda-ll,14-diene-8,13-diols. Some minor products arose from attack at C-12 and include the 12(i )- and 12(5)-labda-13(16)-14-diene-8,12-diols. Reaction of c -abienol with m-chloroperbenzoic acid gave some 8,12- and 8,13-epoxides. The X-ray crystal structure of 12(5),13(S)-8,12 12,15-diepoxy-13-bromolabdane has been determined. The synthesis has been described of some 13,8 13,17-ethers of the enantio-14(15)-dinorlabdane series from eperuic acid. 

Nakano, T., and A. Martin Synthesis of labda-8(17),13(14)-diene-15,16-olide and 15,16-epoxy-labda-8(17),13(16)-14-triene and their rearrangement to clerodane derivatives. Tetrahedron 38, 1217 (1982). 

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