Development of methods suitable for natural product synthesis: The azadirachtin story

Abstract

Our synthesis work on the insect antifeedant azadirachtin is described. Particular emphasis is placed on the key coupling of a left-hand decalin fragment with a right-hand hydroxydihydrofuran acetal unit via a Claisen rearrangement reaction of an intermediate propargylic enol ether. New chemistry has been developed leading to control of an endo-selective intramolecular Diels–Alder reaction using silicon, which was essential for the construction of the appropriately functionalized decalin fragment. In order to install the five-ring hemiacetal of azadirachtin, we also developed a new ring contraction protocol via an intermediate six-ring cyano ester.