Synthesis of Azadirachtin, an insect antifeedant

Azadirachtin (1), which was isolated from the Indian neem tree in 1968, exhibits potent antifeedant and growth inhibitory activities against many insects. Because of its complicated structure, only the Ley group has completed the synthesis of 1. In this article, we describe the second synthesis of 1. The Diels-Alder reaction-decarboxylation-Claisen rearrangement approach was used to construct the basic structure of the left-hand segment. The correct stereochemistry at C4 was established by an oxidative ring-opening reaction and a subsequent aldol reaction. The right-hand segment was prepared from the known cyclopentenone derivative. After a coupling of both segments, the key tandem radical cyclization reaction was performed to elaborate the full carbon framework of 1. The cyclized product could be converted into Ley's intermediate in 9 steps, resulting in the formal synthesis of 1. Our synthesis with a longest linear sequence of 39 steps is highly efficient.