Use of (S)-trans-γ-Monocyclofarnesol as a Useful Chiral Building Block for the Stereoselective Synthesis of Diterpenic Natural Products

Abstract

A comprehensive study of the exploitation of ( S)- trans-γ-monocyclofarnesol as a useful chiral building block for the stereoselective synthesis of natural diterpene derivatives is here described. The farnesol derivative (+)-1 was used as starting material in the preparation of the diterpenes ( S)-dehydroambliol-A and ( S)-trixagol, as well as for the syntheses of the dinorditerpene ( S)-dinortrixagone and of the guanidine-interrupted terpenoid ( S)-dotofide. Key steps of the presented syntheses were the cross-coupling between an allyl acetate and a Grignard reagent, the Wittig reaction, the selective preparation of a diacylguanidine derivative and the alkylation of a sulfone derivative, followed by the reductive removal of the same functional group. It is worth noting that the natural products (+)-8, (+)-12 and (+)-15 were prepared stereoselectively for the first time, thus allowing the unambiguous assignment of their absolute configuration.