Synthetic studies on azadirachtin: construction of the ABC ring system via the Diels–Alder reaction of a vinyl allenylsilane derivative

[Display omitted] Studies toward the asymmetric total synthesis of azadirachtin are explored. The ABC ring system was constructed through the stereoselective Diels–Alder reaction of an optically active vinyl allenylsilane derivative followed by an intramolecular aldol reaction. The highly hindered C8–C14 bond was formed by an intermolecular addition reaction of an aldehyde and the allylborane moiety in the B ring. Cyclization of the E ring moiety by the Pd-catalyzed Nazarov reaction afforded a compound having the highly functionalized ABCE ring system of azadirachtin.