Photoredox-Catalyzed Oxidation of Anions for the Atom-Economical Hydro-, Amido-, and Dialkylation of Alkenes

J Org Chem. 2022 Mar 4;87(5):3498-3510. doi: 10.1021/acs.joc.1c03055. Epub 2022 Feb 8.

Abstract

Photoredox catalysis has become a powerful method to generate free radical intermediates in organic synthesis. This report describes the use of photoredox catalysis to directly oxidize common nucleophilic anions to access electrophilic 1,3-dicarbonyl and amidyl radical intermediates. First, conjugate bases of 1,3-dicarbonyls were oxidized to neutral radical species for intramolecular hydro- and dialkylation of alkenes. This overall redox-neutral process provided cyclopentanone products in excellent yields (up to 96%). The scope included a variety of styrene radical acceptors and products with newly formed vicinal quaternary carbons. This process was then extended to the synthesis of pyrrolidinones by alkene amidoalkylation that proceeded via N-aryl amidyl radical intermediates in good yield (up to 85%). These reactions were characterized by their mild conditions, high atom economy, and the absence of stoichiometric byproducts. Mechanistic and computational studies supported a stepwise proton-coupled electron transfer mechanism, where an "electron borrowing" photocatalyst oxidizes an anion and reduces a benzylic radical after bond formation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alkenes* / chemistry
  • Anions
  • Catalysis
  • Oxidation-Reduction
  • Protons*

Substances

  • Alkenes
  • Anions
  • Protons