Chiral picolylamines for Michael and aldol reactions: probing substrate boundaries

Org Biomol Chem. 2012 Dec 14;10(46):9287-94. doi: 10.1039/c2ob26382c. Epub 2012 Oct 29.

Abstract

Here we report on inroads concerning increased substrate breadth via the picolylamine organocatalyst template, a vicinal chiral diamine based on a pyridine-primary amine motif. The addition of cyclohexanone to β-nitrostyrene has many catalyst solutions, but cyclopentanone and isobutyraldehyde additions continue to be challenging. PicAm-3 (10 mol%) readily allows the Michael addition of cyclopentanone or isobutyraldehyde (5.0 equiv.) to β-nitrostyrene derivatives. By contrast, PicAm-1 (7.0 mol%) is optimal for catalyzing the aldol reaction of cyclohexanone or cycloheptanone (3.3 equiv.) with aromatic aldehydes. Eighteen products are reported and for each reaction type new products are reported (4b-d, 9c). Very good yields and stereoselectivities are generally noted. The reactions, which require an acid additive, proceed via a transient chiral enamine and a mechanistic case is put forth for a bifunctional catalysis model.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aldehydes / chemistry*
  • Catalysis
  • Chromatography, High Pressure Liquid
  • Cyclohexanones / chemistry*
  • Cyclopentanes / chemistry
  • Diamines / chemistry*
  • Molecular Structure
  • Pyridines / chemistry*
  • Spectrometry, Mass, Electrospray Ionization
  • Stereoisomerism
  • Styrenes / chemistry*

Substances

  • Aldehydes
  • Cyclohexanones
  • Cyclopentanes
  • Diamines
  • Pyridines
  • Styrenes
  • cyclopentanone
  • beta-nitrostyrene
  • cyclohexanone
  • 3-hydroxybutanal
  • isobutyraldehyde