Synthetic Progress toward Azadirachtins. 1. Enantio- and Diastereoselective Synthesis of the Left-Wing Fragment of 11-epi-Azadirachtin I

A highly enantio- and diastereoselective synthesis of the left-wing fragment of 11-epi-azadirachtin I characterized with the pairwise use of palladium- and gold-catalyzed cascade reactions is presented. By enlisting a sequence of stereocontrolled transformations, our 21-step route established the stereocenters of the left-wing fragment from one chiral starting material, (−)-carvone, which would significantly facilitate the synthetic studies of the azadirachtin-type limonoids.