Lewis acid-Lewis acid heterobimetallic cooperative catalysis: mechanistic studies and application in enantioselective aza-Michael reaction

J Am Chem Soc. 2005 Sep 28;127(38):13419-27. doi: 10.1021/ja054066b.

Abstract

The full details of a catalytic asymmetric aza-Michael reaction of methoxylamine promoted by rare earth-alkali metal heterobimetallic complexes are described, demonstrating the effectiveness of Lewis acid-Lewis acid cooperative catalysis. First, enones were used as substrates, and the 1,4-adducts were obtained in good yield (57-98%) and high ee (81-96%). Catalyst loading was successfully reduced to 0.3-3 mol % with enones. To broaden the substrate scope of the reaction to carboxylic acid derivatives, alpha,beta-unsaturated N-acylpyrroles were used as monodentate, carboxylic acid derivatives. With beta-alkyl-substituted N-acylpyrroles, the reaction proceeded smoothly and the products were obtained in high yield and good ee. Transformation of the 1,4-adducts from enones and alpha,beta-unsaturated N-acylpyrroles afforded corresponding chiral aziridines and beta-amino acids. Detailed mechanistic studies, including kinetics, NMR analysis, nonlinear effects, and rare earth metal effects, are also described. The Lewis acid-Lewis acid cooperative mechanism, including the substrate coordination mode, is discussed in detail.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aza Compounds / chemical synthesis*
  • Aza Compounds / chemistry
  • Catalysis
  • Ketones / chemical synthesis*
  • Ketones / chemistry
  • Lithium / chemistry*
  • Magnetic Resonance Spectroscopy / methods
  • Magnetic Resonance Spectroscopy / standards
  • Metals, Rare Earth / chemistry*
  • Molecular Structure
  • Organometallic Compounds / chemistry*
  • Reference Standards
  • Stereoisomerism

Substances

  • Aza Compounds
  • Ketones
  • Metals, Rare Earth
  • Organometallic Compounds
  • Lithium