Catalytic, Enantioselective β-Protonation through a Cooperative Activation Strategy

J Org Chem. 2017 May 5;82(9):4689-4702. doi: 10.1021/acs.joc.7b00334. Epub 2017 Apr 25.

Abstract

The NHC-catalyzed transformation of unsaturated aldehydes into saturated esters through an organocatalytic homoenolate process has been thoroughly studied. Leveraging a unique "Umpolung"-mediated β-protonation, this process has evolved from a test bed for homoenolate reactivity to a broader platform for asymmetric catalysis. Inspired by our success in using the β-protonation process to generate enals from ynals with good E/Z selectivity, our early studies found that an asymmetric variation of this reaction was not only feasible, but also adaptable to a kinetic resolution of secondary alcohols through NHC-catalyzed acylation. In-depth analysis of this process determined that careful catalyst and solvent pairing is critical for optimal yield and selectivity; proper choice of nonpolar solvent provided improved yield through suppression of an oxidative side reaction, while employment of a cooperative catalytic approach through inclusion of a hydrogen bond donor cocatalyst significantly improved enantioselectivity.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Aldehydes / chemistry*
  • Catalysis
  • Oxidation-Reduction
  • Protons
  • Stereoisomerism

Substances

  • Aldehydes
  • Protons