Asymmetric aldol reaction of 2-cyanopropionates catalyzed by a trans-chelating chiral diphosphine-rhodium(I) complex:: highly enantioselective construction of quaternary chiral carbon centers at α-positions of nitriles

The aldol reaction of 2-cyanopropionates with aldehydes proceeded under neutral conditions in the presence of a catalytic amount of the rhodium complex generated in situ from Rh(acac)(CO)(2) and triphenylphosphine, to give the corresponding beta-hydroxy-alpha-cyanocarboxylates bearing a quaternary chiral carbon center at the alpha-position of the cyano group. A high degree of asymmetric induction for the aldol reaction was achieved by use of trans-chelating chiral diphosphine ligands, (R,R)-2,2-bis[(S)-1 -(diarylphosphino)ethyl]-1,1-biferrocenes (TRAPs). The asymmetric aldol reactions gave optically active beta-hydroxy-alpha-cyanocarboxylates with up to 94% ee. (C) 2000 Elsevier Science S.A. All rights reserved.