Toward the Asymmetric Synthesis of Cardenolides and Related Steroidal Systems: syn-SN2′ of Organometallics with C14–C17 Vinylepoxides

In a program aimed at establishing a common sequence of C–C bond-forming reactions for asymmetric construction of tetracyclic triterpenoid natural products and related synthetic systems, effort has been directed toward introducing C17β-substitution by late-stage functionalization of stereodefined “steroidal” D-ring vinylepoxides (spanning C14–C17). It has been found that cyanocuprates participate in syn-SN2′ reactions that result in products bearing various C17β-substituents and containing a β-OH at C14.