Synthetic studies on the preparation of oxygenated spongiane diterpenes from carvone

The paper describes a new diastereoselective approach to oxygenated spongiane diterpenes functionally related to natural dorisenones. The strategy followed for the preparation of the spongiane framework, a B-->AB-->ABC-->ABCD approach, is based on the preparation of epoxydecalone 11 (AB rings) from R-(-)-carvone, followed by an intramolecular Diels-Alder reaction for the construction of the C ring (compound 26). Further manipulation of the Diels-Alder adduct functionality allows the completion of the spongiane framework and the elaboration of several oxygenated spongiane-type compounds. The structures of two compounds 27 and 31, has been established by single-crystal X-ray crystallography. (C) 2003 Elsevier Ltd. All rights reserved.