Gold-Catalyzed Enantio- and Diastereoselective Syntheses of Left-Fragments of Azadirachtin/Meliacarpin-Type Limonoids.

Meliacarpin-type limonoids are an important class of organic insecticides. The syntheses are challenging due to the chemical complexity. Here, we report the highly enantio- and diastereo-selective synthesis of the left-fragments of azadirachtin I and 1-cinnamoylmelianolone, being two important family members of meliacarpin-type limonoids, via pair-wise palladium- and gold-catalyzed cascade reactions. Gold-catalyzed reactions of 1,7-diynes were performed as model studies, and the efficient construction of tetracyclic late-stage intermediates was achieved based on this key transformation. Our unique route gave both the left-fragments in 23 steps from the commercially available chiral starting material (-)-carvone. This study significantly advances research on the synthesis of the meliacarpin-type limonoids.