16O/18O Exchange of Aldehydes and Ketones caused by H2 18O in the Mechanistic Investigation of Organocatalyzed Michael, Mannich, and Aldol Reactions

Yujiro Hayashi, Takasuke Mukaiyama, Meryem Benohoud, Nishant R. Gupta, Tsuyoshi Ono, Shunsuke Toda

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

Organocatalyzed Michael, Mannich, and aldol reactions of aldehydes or ketones, as nucleophiles, have triggered several discussions regarding their reaction mechanism. H2 18O has been utilized to determine if the reaction proceeds through an enamine or enol mechanism by monitoring the ratio of 18O incorporated into the final product. In this communication, we describe the risk of H2 18O as an evaluation tool for this mechanistic investigation. We have demonstrated that exchange of 16O/18O occurs in the aldehyde or ketone starting material, caused by the presence of H2 18O and amine catalysts, before the Michael, Mannich, and aldol reactions proceed. Because the newly generated 18O starting aldehydes or ketones and 16O water affect the incorporation ratio of 18O in the final product, the use of H2 18O would not be appropriate to distinguish the mechanism of these organocatalyzed reactions. Exchange of 16O/18O occurs in the aldehyde or ketone starting material in the presence of H2 18O and amine catalysts before the organocatalyzed Michael, Mannich, and aldol reactions proceed. Because the newly generated 18O starting aldehyde or ketone and 16O water affect the incorporation ratio of 18O in the final product, the use of H2 18O would not be appropriate for distinguishing between the enamine and enol pathway for these types of transformation (see scheme).

Original languageEnglish
Pages (from-to)5868-5872
Number of pages5
JournalChemistry - A European Journal
Volume22
Issue number17
DOIs
Publication statusPublished - 2016 Apr 18

Keywords

  • asymmetric synthesis
  • enamines
  • enols
  • organocatalyst
  • reaction mechanisms

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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