Asymmetric Michael reaction of α-cyano carboxylates catalyzed by a rhodium complex with trans-chelating chiral diphosphine PhTRAP

Abstract

Asymmetric Michael reaction of 2-cyanopropionates with vinyl ketones or acrolein in the presence of 0.1–1 mol% of a rhodium catalyst prepared in situ from RhH(CO)(PPh 3) 3 and a trans-chelating chiral diphosphine ligand ( S,S)-( R,R)-PhTRAP in benzene at 3–5°C gave optically active Michael adducts with high enantiomeric excesses (83–93% ee) in high yields. The reaction of 2-cyanopropionate with methacrolein and crotonaldehyde proceeded somewhat slowly, giving diastereomer mixtures in moderate enantioselectivities but in low diastereoselectivities. The reaction of 2-cyanobutyrate and 2-cyano-3-methylbutyrate with acrolein gave corresponding Michael adducts with much lower enantiomeric excesses than that of 2-cyanopropionates. The Michael addition product from acrolein was converted into an optically active α-methyl-α-amino acid.