Synthesis of BCD tricyclic analogues of the novel cardiac glycoside rhodexin A

A concise synthesis of novel cardiac glycoside analogues of rhodexin A, 14 and 24, having the BCD tricyclic system is described. The key constructive step is an inverse-electron demand Diels–Alder reaction of the silyl enol ether 4 and the 2-acetyldiene, 7 and 15.