Novel and efficient synthesis of rotenoids via intramolecular radical arylation

Abstract

Treatment of the iodoarylchromenes 22 with palladium acetate gave the tetracyclic compounds 23via a formal but stereochemically disallowed Heck reaction; a crystalline intermediate palladium species 25(X-ray analysis) was isolated. The method was employed to synthesise the natural rotenoid (±)-munduserone 29. Related reductive radical cyclisation of enol acetate 31 gave the (±)-6aα,12a,12aα-chromenochromenol acetate 32(R = Ac), representing the core structure of the insecticidal rotenoid 2, in a 5 step (15% overall) route from 2-methylthiomethylchromone 17. The cis,cis-geometry is obtained stereospecifically through an intramolecular 6-exo addition mode.