Application of a new amidophosphite ligand to Rh‐catalyzed asymmetric hydrogenation of β‐dehydroamino acid derivatives in supercritical carbon dioxide: Activation effect of protic co‐solvents

Abstract

New chiral amidophosphite ligand was synthesized and tested in the Rh-catalyzed asymmetric hydrogenation of (Z)-β-(acylamino)acrylates in protic solvents and supercritical carbon dioxide (scCO(2) ) The catalytic performance is affected greatly by the acidity of the solvents. Better enantioselectivity (up to 88% ee) was achieved in scCO(2) containing 1,1,1,3,3,3-hexafluoro-2-propanol, compared to neat protic solvents.

HFIP in Organic Synthesis

“…A rhodium (Rh)-catalyzed asymmetric hydrogenation of a small set of ( Z )-β-(acylamino)­acrylates using a chiral amidophosphite ligand in supercritical carbon dioxide (scCO 2 ) with HFIP as a cosolvent resulted in complete conversions to the corresponding β-amino acids with good enantioselectivities (Scheme ). , The significant improvements in the enantioselectivity and conversion with HFIP compared to methanol (MeOH) and i -PrOH were attributed to its increased acidity and stronger hydrogen-bond donor ability, which, by interrupting the intramolecular hydrogen bond in the substrates, allowed coordination of the chiral catalyst complex and permitted the asymmetric hydrogenation to proceed. A similar Rh-catalyzed asymmetric hydrogenation in HFIP using a chiral carboranylamidophosphite ligand provided high conversions to the desired β-amino acids with modest to good enantioselectivities (46–85% ee) .…”