Phase-transfer-catalyzed asymmetric acylimidazole alkylation

Org Lett. 2007 Nov 8;9(23):4865-8. doi: 10.1021/ol702197r. Epub 2007 Oct 18.

Abstract

2-Acylimidazoles are alkylated under phase-transfer conditions with cinchonidinium catalysts at -40 degrees C with allyl and benzyl electrophiles in high yield with excellent enantioselectivity (79 to >99% ee). The acylimidazole substrates are made in three steps from bromoacetic acid via the N-acylmorpholine adduct. The catalyst is made in high purity allowing for S-product formation (6-20 h) under mild conditions, consistent with an ion-pair mechanism. The products are readily converted to useful ester products using methyltriflate and sodium methoxide, via a dimethylacylimidazolium intermediate without racemization. The process is efficient, direct, and amenable to other electrophiles and transformations that proceed through an enolate intermediate.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acylation
  • Alkylation
  • Benzene / chemistry
  • Catalysis
  • Electrons
  • Esters / chemistry
  • Imidazoles / chemical synthesis*
  • Imidazoles / chemistry
  • Methylation
  • Molecular Structure
  • Phase Transition
  • Stereoisomerism

Substances

  • Esters
  • Imidazoles
  • imidazole
  • Benzene