Helenanolides: Stereocontrolled Total Synthesis of dl-Bigelovin, dl-Mexicanin I, and dl-Linifolin A

Article abstract of DOI:10.1021/jo00151a016

Stereocontrolled total syntheses of the sesquiterpene lactones dl-bigelovin (11), dl-mexicanin I (12), and dl-linifolin A (13) are described.The syntheses start with the hydroazulenone 4 and proceed via the key epoxy alkohol 9.Elaboration of 9 into the tricyclic γ-lactone 14 dl-bigelovin. α-methylenation.Subsequent oxidation at C(4) completes the synthesis of dl-bigelovin.Epoxide opening of 9 with dilithioacetate provides access to tricyclic lactone 23 which gives way to 24 via reduction of ketone 25.Cleavage of the benzyl ether in 24 followed by α-methylenationand oxidation generates dl-mexicanin I.Acetylation of 12 affords dl-linifolin A.