Asymmetric synthesis. Asymmetric catalytic hydrogenation using chiral chelating six-membered ring diphosphines

Abstract

Rhodium(I) catalysts formed by the two chiral chelating six-membered ring diphosphines, 2,4-bis(diphenylphosphino)pentane (skewphos) and l,3-bis(diphenylphosphino)butane (chairphos), are efficient catalysts for the hydrogenation of amino acid precursors. The two chiral phosphines differ in that skewphos probably adopts a chiral conformation whereas chairphos probably adopts an achiral conformation. As a consequence the former generally gives high optical yields whereas the latter is ineffective as a chiral catalyst. This comparison evidences the importance of ring conformations in determining optical yields. The mechanism of asymmetric hydrogenation is discussed, and a number of particular and general conclusions are drawn which may prove useful in predicting optical yields from asymmetric synthesis.

Enantioselective Hydrogenation of β‐Keto Esters using Chiral Diphosphine‐Ruthenium Complexes: Optimization for Academic and Industrial Purposes and Synthetic Applications

“…This universal synthetic method allows the production of ruthenium complexes from a wide variety of diphosphines including DIOP, [11] DIPAMP, [12] CHIRAPHOS, [13] BDPP, [14] BIPNOR, [15] BINAP, [16] Tol-BINAP, [17] MeO-BI-PHEP [18] and more recently cationic Digm-BINAP, [19] to quote a few examples. The in situ generated chiral Ru(II)-catalysts have been used by our group [9] and others [20] in very efficient asymmetric hydrogenation reactions of b-keto esters and various substrates both at atmospheric and higher pressures.…”

Solid-Phase Synthesis and Catalytic Screening of Polystyrene Supported Diphosphines

“…Surprisingly for substrate I and III the (R) product was observed whereas 9d with the same absolute configuration provides the (S) product. However, for substrate II the expected opposite enantiomer (S) was c Data taken from Ref [42]; reaction performed at p (H 2 ) = 5 bar in MeOH d Data taken from Ref [43] e Data taken from Ref [44] Top Catal (2016) 59:1793-1799 1797 obtained again. For ligands 9d and e changing the configuration of the ligand backbone led as expected to the opposite configuration of the products in catalysis for all three of the substrates.…”

(R,R)-N-phenyl-3,4-bis(diphenylphosphino)pyrrolidine: an N-aryl pyrrolidine ligand for enantioselective transfer hydrogenation

“…The exact orientation of these groups in the catalyst is dependant on the chiral conformation of each ligand which in turn is determined by the backbone structure in each particular case [28][29][30][31][32][33][34][35][36]. The phenyl group directly bonded to the nitrogen in 2 confers upon this atom significant sp 2 character as can be confirmed by bond angles C1A-N1-C5, 122.5(3); C1A-N1-C2, 124.2(3); and C5-N1-C2, 112.5(3) as well as the N1-C1A bond length, 137.0(5) pm.…”