Development of methods suitable for natural product synthesis: The azadirachtin story*
Steven V. Ley
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
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.
Keywords: natural product synthesis; azadirachtin; endo-selective intramolecular Diels–Alder; decalin; hydroxyfuranacetal.
*An issue of reviews and research papers based on lectures presented at the 15th International Conference on Organic Synthesis (ICOS-15), held in Nagoya, Japan, 1-6 August 2004, on the theme of organic synthesis. Other presentations are published in this issue, pp. 1087-1296.