Highly Diastereoselective Synthesis of 2-(1-N-Boc-aminoalkyl)thiazole-5-carboxylates by Reduction of tert-Butylsulfinyl Ketimines

Chem Pharm Bull (Tokyo). 2018;66(4):416-422. doi: 10.1248/cpb.c17-00907.


Positional isomers of naturally occurring peptide subunits were synthesized via highly diastereoselective reduction of tert-butylsulfinyl ketimines as a key reaction. While NaBH4 reduction of ketimines derived from 2-thiazolyl ketones afforded the (RS,R)-isomer with moderate diastereoselectivity, L-Selectride® reduction afforded the (RS,S)-isomer as the sole product. In contrast, ketimines derived from tert-butyl 2-thiazolyl ketone afforded the (RS,R)-isomer with low diastereoselectivity by both NaBH4 and L-Selectride® reduction. Stereochemistry of the reaction was discussed based on calculation of the conformational energies for ketimines.

Keywords: L-Selectride; N-tert-butylsulfinyl ketimine; thiazole amino acid.

MeSH terms

  • Imines / chemistry*
  • Molecular Structure
  • Nitriles / chemistry*
  • Oxidation-Reduction
  • Stereoisomerism
  • Thiazoles / chemical synthesis*
  • Thiazoles / chemistry


  • Imines
  • Nitriles
  • Thiazoles
  • ketimine