Biomimetic syntheses of C23 terpenoids: structural revision of salyunnanin A and confirmation of hassanane

Abstract

Salyunnanin A and hassanane, two C₂₃ terpenoids, were achieved from (+)-carnosic acid in 6 and 5 steps, respectively. The synthetic strategy was primarily inspired by the biogenetic hypothesis and provided access to the natural products via elimination, double Michael-type addition in one pot to prepare the corresponding 6,20-epoxyabietanes, and bismuthonium ylide induced ring expansion of o-quinone to construct 2-acyl-3-hydroxytropone.