Catalytic kinetic resolution of a dynamic racemate: Highly stereoselective β-lactone formation by N-heterocyclic carbene catalysis

Ryne C. Johnston, Daniel T. Cohen, Chad C. Eichman, Karl A. Scheidt*, Paul Ha-Yeon Cheong

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

51 Scopus citations

Abstract

This study describes the combined experimental and computational elucidation of the mechanism and origins of stereoselectivities in the NHC-catalyzed dynamic kinetic resolution (DKR) of α-substituted-β- ketoesters. Density functional theory computations reveal that the NHC-catalyzed DKR proceeds by two mechanisms, depending on the stereochemistry around the forming bond: (1) a concerted, asynchronous formal (2 + 2) aldol-lactonization process, or (2) a stepwise spiro-lactonization mechanism where the alkoxide is trapped by the NHC-catalyst. These mechanisms contrast significantly from mechanisms found and postulated in other related transformations. Conjugative stabilization of the electrophile and non-classical hydrogen bonds are key in controlling the stereoselectivity. This reaction constitutes an interesting class of DKRs in which the catalyst is responsible for the kinetic resolution to selectively and irreversibly capture an enantiomer of a substrate undergoing rapid racemization with the help of an exogenous base.

Original languageEnglish (US)
Pages (from-to)1974-1982
Number of pages9
JournalChemical Science
Volume5
Issue number5
DOIs
StatePublished - May 2014

ASJC Scopus subject areas

  • Chemistry(all)

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