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Understanding the Mechanism of the Intramolecular Stetter Reaction. A DFT Study
Departamento de Química Orgánica, Universidad de Valencia, Dr. Moliner 50, E-46100 Burjassot, Valencia, Spain
* Author to whom correspondence should be addressed.
Received: 22 December 2011; in revised form: 19 January 2012 / Accepted: 20 January 2012 / Published: 2 February 2012
Abstract: The mechanism of the N-heterocyclic carbene (NHC)-catalyzed intramolecular Stetter reaction of salicylaldehyde 1 to yield chromanone 3 has been theoretically studied at the B3LYP/6-31G** level. This NHC-catalyzed reaction takes place through six elementary steps, which involve: (i) formation of the Breslow intermediate IN2; (ii) an intramolecular Michael-Type addition in IN2 to form the new C-C s bond; and (iii) extrusion of the NHC catalyst from the Michael adduct to yield chromanone 3. Analysis of the relative free energies in toluene indicates that while formation of Breslow intermediate IN2 involves the rate-determining step of the catalytic process, the intramolecular Michael-type addition is the stereoselectivity determining step responsible for the configuration of the stereogenic carbon a to the carbonyl of chromanone 3. An ELF analysis at TSs and intermediates involved in the Michael-type addition allows for the characterization of the electronic changes along the C-C bond-formation.
Keywords: organocatalysis; N-heterocyclic carbenes; umpolung reactivity; intramolecular Stetter reaction; intramolecular Michael addition; mechanisms; DFT calculations
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Domingo, L.R.; Zaragozá, R.J.; Saéz, J.A.; Arnó, M. Understanding the Mechanism of the Intramolecular Stetter Reaction. A DFT Study. Molecules 2012, 17, 1335-1353.
Domingo LR, Zaragozá RJ, Saéz JA, Arnó M. Understanding the Mechanism of the Intramolecular Stetter Reaction. A DFT Study. Molecules. 2012; 17(2):1335-1353.
Domingo, Luis R.; Zaragozá, Ramón J.; Saéz, Jose A.; Arnó, Manuel. 2012. "Understanding the Mechanism of the Intramolecular Stetter Reaction. A DFT Study." Molecules 17, no. 2: 1335-1353.