Asymmetric catalytic reduction with transition metal complexes. I. Catalytic system of rhodium(I) with (-)-2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane, a new chiral diphosphine

Abstract

The catalytic system (-)-(diop)-Rh(I) (diop = 2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane (7)) is described and is used for an extensive study of the hydrogenation of various precursors of alanine, phenylalanine, tyrosine, Dopa, and leucine. Optical yields in the range of 70-80 % are obtained in the reduction of ^-substituted -acetamidoacrylic acids. The presence of a carboxyl group is found not to be absolutely necessary for good optical yield. The favorable effect of the enamide function on the catalytic process is deduced from comparisons of the rates of hydrogenation of atropic and acetamidocinnamic acids, from the optical yields obtained in the reduction of different precursors of phenylalanine, and from the high optical yield (78 %) obtained in the hydrogenation of the enamide 12, a compound having no carboxyl groups.

On the Synthesis and Addition Reactions of Chiral N-Heterocyclic Diphosphines

“…Further reaction of 11 with acrylonitrile generated a mixture of altogether four products with intensity ratios close to 1 : 1 : 1 : 1 (determined by integration of 31 P NMR signals), which were found to be unseparable by crystallization. The AX-and AMX-type splittings in 31 P{ 1 H} and 31 P NMR spectra (with δ 31 P = 95 -97 for PN 2 and −22 to −43 for P(H)Men groups), respectively, are retained but exhibit much smaller values of J PP (10 -32 Hz) than in 11, thus supporting the structural assignment as diastereomeric 1,2-bisphosphines 12 (Scheme 3). The observed intensity distribution complies with the presence of a statistical mixture of diastereomers having different configuration at the stereogenic phosphorus and backbone carbon atoms, which leads us to conclude that all possible isomers are very similar in energy.…”

“…Some prominent examples of chiral bidentate phosphines include Kagan's DIOP [2], Knowles' DIPAMP [3], or Noyori's BINAP [4 -8], all of which became key components of many transition metal catalysts that are now widely used in organic and organometallic chemistry. Chirality is introduced into the structure of these ligands in several ways, viz.…”

Asymmetric Hydrogenation

“…The ligand, 4,5-bis[(diphenylphosphino)methyl]-2,2-dimethyl-1,3-dioxolane (DIOP), is the first example of a C2-symmetric phosphine ligand. Its high capacity for asymmetric induction, up to 88%, was demonstrated in the hydrogenation of -dehydroamino acids and enamides [5], and these excellent results stimulated the design and synthesis of many other C2-symmetric phosphine ligands. The most notable ligand reported in the period up to 1979 was 1,2-bis(o-anisylphenylphosphino)ethane (DIPAMP) developed by Knowles (Nobel laureate in 2001) et al at Monsanto in 1975, which provided very high enantioselectivity values up to 96% in the hydrogenation of -dehydroamino acids [6].…”

Prix Nobel de chimie 2001 : William S. Knowles, Ryoji Noyori, K. Barry Sharpless

“…Sans être cocardier, on peut considérer que Henri Kagan a joué un rôle majeur dans la catalyse asymétrique. Il a en effet été le premier à valider le concept des phosphines comme ligand de métaux, notamment par l'introduction du catalyseur DIOP [6]. De plus, il a montré l'importance de la symétrie axiale C2 du catalyseur (figure 2).…”