A higher energy conformer of (S)-proline is the active catalyst in intermolecular aldol reaction: Evidence from DFT calculations

Manjaly J. Ajitha, Cherumuttathu H. Suresh*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

Full catalytic cycle of the stereoselective (S)-proline catalyzed aldol reaction of acetone and acetaldehyde in DMSO solvent has been investigated using three different DFT methods, viz. B3LYP, MPWB1K and B97D in conjunction with the polarizable continuum (PCM) method. At all the levels of theory, one of the higher energy conformers of the catalyst, 1b showed higher activity than the most stable conformer, 1a. On the basis of ΔG# of 39.8 kcal/mol observed for the reaction of 1a with acetone, 1a is considered to be inactive in the catalytic cycle while the same reaction with 1b showed 22.7 kcal/mol (B97D-PCM level) lower value for ΔG# than 1a. All the possibilities for enamine formation and C-C bond formation step have been considered for describing the most appropriate stereoselective catalytic cycle which showed that the full cycle is made up of a relay of eight proton transfer steps and the reaction is categorized under hydrogen bond catalysis. The hydration across the iminium bond of the second nucleophilic adduct - an intermediate formed subsequent to the aldehyde addition to the enamine - is the rate limiting step of the reaction with ΔG# = 21.7 kcal/mol (B97D-PCM level).

Original languageEnglish (US)
Pages (from-to)37-43
Number of pages7
JournalJournal of Molecular Catalysis A: Chemical
Volume345
Issue number1-2
DOIs
StatePublished - Jul 5 2011

Bibliographical note

Funding Information:
This research is supported by Council of Scientific and Industrial Research (CSIR), India . A.M.J. is thankful to UGC, Government of India for providing research fellowship. The authors are also thankful to Prof. G. Frenking for fruitful discussions.

Keywords

  • (S)-Proline
  • Aldol reaction
  • Dispersion-corrected DFT
  • Hydrogen bond catalysis
  • Organocatalysis
  • Proton transfer mechanism

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology
  • Physical and Theoretical Chemistry

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