The Thermal Cyclisation of Unsaturated Carbonyl Compounds

Abstract

When heated, in a sealed tube or in the vapour phase (250° −380°), unsaturated carbonyl compounds of suitable geometry (e-ethylenic ketones among others) undergo, in their enol form, an intramolecular ene reaction. In this reaction the enol hydrogen is shifted to the terminal carbon atom of the unsaturated center and cyclisation occurs by σ bonding between the other carbon atom of that center and the carbon atom α with respect to the carbonyl group. Such cyclisation is general, and very simple and its interest in synthesis in alicyclic chemistry is clear.