On the role of pre- and post-electron-transfer steps in the SmI 2/Amine/H2O-mediated reduction of esters

New mechanistic insights and kinetic studies

Michal Szostak, Malcolm Spain, David J. Procter

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

The mechanism of the SmI2-mediated reduction of unactivated esters has been studied using a combination of kinetic, radical clocks and reactivity experiments. The kinetic data indicate that all reaction components (SmI2, amine, H2O) are involved in the rate equation and that electron transfer is facilitated by Brønsted base assisted deprotonation of water in the transition state. The use of validated cyclopropyl-containing radical clocks demonstrates that the reaction occurs via fast, reversible first electron transfer, and that the electron transfer from simple Sm(II) complexes to aliphatic esters is rapid. Notably, the mechanistic details presented herein indicate that complexation between SmI2, H2O and amines affords a new class of structurally diverse, thermodynamically powerful reductants for efficient electron transfer to carboxylic acid derivatives as an attractive alternative to the classical hydride-mediated reductions and as a source of acyl-radical equivalents for C-C bond forming processes. Electron donors: The mechanism of the SmI 2-mediated reduction of unactivated esters has been studied by using a combination of kinetic, radical clock, and reactivity experiments. Notably, the mechanistic details presented herein indicate that complexation between SmI2, H2O, and amines gives a new class of structurally diverse, thermodynamically powerful reductants for efficient electron transfer to carboxylic acid derivatives as an attractive alternative to the classical hydride-mediated reductions and as a source of acyl-radical equivalents for C-C bond-forming processes (see scheme).

Original languageEnglish (US)
Pages (from-to)4222-4226
Number of pages5
JournalChemistry - A European Journal
Volume20
Issue number15
DOIs
StatePublished - Apr 7 2014

Fingerprint

Amines
Esters
Kinetics
Electrons
Clocks
Reducing Agents
Carboxylic Acids
Complexation
Carboxylic acids
Hydrides
Derivatives
Deprotonation
samarium diiodide
Experiments
Water

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Organic Chemistry

Keywords

  • electron donors
  • electron transfer
  • radicals
  • reduction
  • reductive coupling

Cite this

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On the role of pre- and post-electron-transfer steps in the SmI 2/Amine/H2O-mediated reduction of esters : New mechanistic insights and kinetic studies. / Szostak, Michal; Spain, Malcolm; Procter, David J.

In: Chemistry - A European Journal, Vol. 20, No. 15, 07.04.2014, p. 4222-4226.

Research output: Contribution to journalArticle

TY - JOUR

T1 - On the role of pre- and post-electron-transfer steps in the SmI 2/Amine/H2O-mediated reduction of esters

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