Jump to main content
Jump to site search


A theoretical study on NHC-catalysed enantioselective cycloaddition of ketenes and 3-aroylcoumarins: mechanism and enantioselectivity

Author affiliations

Abstract

NHC-catalysed enantioselective cycloaddition of ketenes to 3-aroylcoumarins to yield dihydrocoumarin-fused dihydropyranones has been investigated using DFT methods at the B3LYP/6-31G* and MPWB1K/6-311G** computational levels. Two plausible mechanisms have been studied: the “ketene-first” mechanism A and the “coumarin-first” mechanism B. An analysis of the activation Gibbs free energies involved in the two competitive pathways makes it possible to rule out the pathway associated with the “coumarin-first” mechanism B. The first step of the “ketene-first” mechanism A is the formation of zwitterionic intermediate IN1-Z via a nucleophilic attack of NHC 1 on ketene 2. A [4 + 2] cycloaddition through the nucleophilic attack of enolate IN1-Z on the conjugated double bond of the benzoyl group of coumarin 3, via TS3-SS-a2 or TS3-RR-a2, yields IN3. Finally, the extrusion of the catalyst through TS5 leads to the final products, either 4-SS or 4-RR. Enantioselectivity observed in the experimental results is determined in the transition states TS3-SS-a2/TS3-RR-a2. In this pathway, the intramolecular hydrogen-bonding between the hydroxyl group of the IN1-Z adduct and the carbonyl oxygen of the original ketene group directs the final stereochemistry throughout the entire process.

Graphical abstract: A theoretical study on NHC-catalysed enantioselective cycloaddition of ketenes and 3-aroylcoumarins: mechanism and enantioselectivity

Back to tab navigation

Supplementary files

Publication details

The article was received on 03 May 2018, accepted on 11 Jul 2018 and first published on 11 Jul 2018


Article type: Paper
DOI: 10.1039/C8OB01035H
Citation: Org. Biomol. Chem., 2018, Advance Article
  •   Request permissions

    A theoretical study on NHC-catalysed enantioselective cycloaddition of ketenes and 3-aroylcoumarins: mechanism and enantioselectivity

    R. J. Zaragozá, M. J. Aurell and M. A. González-Cardenete, Org. Biomol. Chem., 2018, Advance Article , DOI: 10.1039/C8OB01035H

Search articles by author

Spotlight

Advertisements