Science of Synthesis

Terada, M., Science of Synthesis: Stereoselective Synthesis, (2011) 3, 309.

General Introduction

The ene reaction can be broadly classified as a six-electron pericyclic process that involves the addition of an alkene (ene) with an allylic hydrogen atom to an electron-deficient multiple bond (enophile) (‌Scheme 1‌).[‌1‌–‌15‌] The reaction is accompanied by the migration of the double bond through a 1,5-hydrogen shift, in which the activation energy is significantly larger than for the mechanistically related Diels–Alder cycloaddition. Although high reaction temperatures are generally required to promote the thermal reaction, Lewis acid catalysis enables the reactions to be carried out under milder conditions with significant rate enhancements. Since the inception of Lewis acid catalysis, significant progress has been made in the area of both intra- and intermolecular ene reactions using carbonyl compounds and electron-deficient alkynes, as well as alkenes as enophiles. To date, ene reactions have received considerable attention, since they permit the formation of C—C and C—X bonds (X = heteroatom) using simple and unmodified alkenes, which constitutes an atom-economical process.

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References