Intramolecular electrocyclic reactions. Part II. Reactions of 1,5-di-phenylpenta-1,4-dien-3-one

Abstract

An intramolecular electrocyclic reaction of 1,5-diphenylpenta-trans-1,trans-4-dien-3-one as the cation (generated with acetylium ions) affords, by conrotatory cyclisation, 2-acetoxy-trans-4,5-diphenylcyclopent-2-enyl sodium sulphate (XI), which is hydrolysed by hot 2N-sodium hydroxide or sodium carbonate solution with concomitant pinacolic change to 5-hydroxy-2,3-diphenylcyclopent-2-enone (X), sodium acetate, and sodium sulphite. Generation of the same cation with hydriodic acid gives, by conrotatory cyclisation and reduction, trans-3,4-di-phenylcyclopentanone (VII) in 13% yield.