An asymmetric synthesis of aza analogues of the tricyclic skeleton of daphnane and the ABC ring system of phorbol

An asymmetric synthesis of aza analogues of the ABC ring system of phorbol and related compounds containing the 5-7-6-fused framework of daphnane involved construction of the central seven-membered ring by a regioselective reduction of a chiral imide and cyclization with trifluoromethanesulfonic acid. Subsequent demethylation and oxidative dearomatization of ring C afforded an enantiopure dienone 20 with the same relative and absolute configuration at the 9- and 10-positions of the phorbol skeleton.