Studies toward the Synthesis of Azadirachtin,Part 1:Total Synthesis of a Fully Functionalized ABC Ring Framework and Coupling with a Norbornene Domain

摘要

We recently embarked on a program directed towards the total synthesis of azadirachtin (1,Scheme 1),the remarkable antifeedant agent isolated from the Neem tree'11 and currently in use as an insecticide.'2' Our radical-based approach towards this unusually challenging target molecule (see Scheme 1) was validated by a number of model studies,'3 5' which,however,left much to be desired in terms of functionalities on the crowded decalin system of the natural product.Herein we report the total synthesis of a fully functionalized ABC decalin intermediate 3 and its coupling with a suitable norbornene system 4 to afford a C7-C13 linked product,which was elaborated into the advanced intermediate 2 and whose structural disposition might allow its eventual conversion into azadirachtin (1).In the following Communication in this issue,16' we describe both the total synthesis and semisynthesis of a different decalin intermediate and its elaboration into a close precursor of the target molecule,as well as some interesting reactions made possible by the special proximity effects that uniquely characterize the azadirachtin structural motif.