Chemistry of insect antifeedants from Azadirachta indica(part 13): on the use of the intramolecular Diels–Alder reaction for the construction of trans-fused hydrobenzofuran fragments for azadirachtin synthesis

Abstract

This paper describes a detailed analysis of the influence of various substituents on the stereochemical outcome of the intramolecular Diels–Alder cyclisation of a number of ether-linked trienes. In particular, the role of diene planarity in governing reaction synchronicity and related twist asynchronicity is delineated. Additionally, the controlling influence of a large dimethyl(phenyl)silyl substituent on the dienophile portion of the triene is also explored. A detailed transition-state analysis is given together with X-ray structures for compounds 41 and 46.