β- and σ-Amino acids (2,3- and 3,4-trans-CHA) as catalysts in Knoevenagel condensation and asymmetric aldol reactions

Abstract

The efficacy of the β-and δ-amino acids (5S,6S)-6-amino-5-hydroxycyclohexa-1,3-dienecarboxylic acid (2,3-trans-CHA) and (3R,4R)-4-amino-3-hydroxycyclohexa-1,5-dienecarboxylic acid (3,4-trans-CHA) as catalysts in Knoevenagel condensation and aldol addition reactions is studied. Synthesis of the zinc(II) complexes of 2,3-and 3,4-trans-CHA provided precipitated material of sufficient purity for use. The catalytic Knoevenagel reactions were carried out with the β-amino acid 2,3-trans-CHA and the δ-amino acid 3,4-trans-CHA, resulting in a product yield of up to 61%. The asymmetric aldol addition reactions were carried out with catalytic amounts of the zinc(II) complexes of 2,3-and 3,4-trans-CHA. In this case, it was observed that the ee of the product (up to 90%) depends on the conversion and/or the reaction time.