Intramolecular β-Alkylation of Michael Acceptors

Significance

Nucleophile-catalyzed reactions of Michael acceptors normally give rise to α-substituted products, for example in the Baylis-Hillman reaction. This paper now describes the intramolecular β-alkylation of α,β-unsaturated esters, amides, and nitriles with bromide, tosylate and even chloride as suitable leaving groups. N-Heterocyclic carbenes are employed as catalysts to produce four-, five-, and six-membered rings. The authors propose the reaction to be initiated by the addition of the catalyst to the β-carbon of the Michael acceptor, thereby generating an enolate (A). This undergoes tautomerization to B, which, after intramolecular S_N2 reaction and elimination, affords the product.