Syntheses of oxygenated spongiane diterpenes from carvone. Synthesis of dorisenone C

The synthesis of dorisenone C, a representative member of the spongiane-type diterpene family, is described. The synthesis follows a B→AB→ABC→ABCD approach and is based on the initial preparation of the previously known hydroxy-aldehyde 14 (AB rings) from R-(−)-carvone, followed by an intramolecular Diels-Alder reaction between an oxygenated diene moiety and an acetylenic dienophile for the construction of the C ring (compound 22), and adequate manipulation of the Diels-Alder adduct functionality for completion of the spongiane framework.