Chiral phosphine-phosphinites

Recent developments in chirality induced by ligands, and in efficient synthetic methods for ligands such as diphosphines, chiral diamines, amino-phosphine-phosphinites, phosphino-oxazolines and diimino-diphosphines, are available in the literature.105-107... 

In contrast to the extensive studies on phosphine-phosphites, the corresponding phosphine-phosphinites are rarely exploited. Laschat introduced this design with a bicydic chiral skeleton derived from (lS)-(+)-camphorsulfonic acid [127]. The Rh-complex based on dimesitylphosphinite 154b was found to be the most reactive catalyst, and was used to produce methyl N-2-acetamidodnnamate, with 89% ee. 

Rhodium (I) complexes of chiral phosphines have been the archetypical catalysts for the hydrocarbonylation of 1-alkenes, with platinum complexes such as (61) making an impact also in the early 1990s[1461. More recently, rhodium(I)-chiral bisphosphites and phosphine phosphinites have been investigated. Quite remarkable results have been obtained with Rh(I)-BINAPHOS (62), with excellent ee s being obtained for aldehydes derived for a wide variety of substrates1 471. For example, hydroformylation of styrene gave a high yield of (R)-2-phenylpropanal (94% ee). The same catalyst system promoted the conversion of Z-but-2-ene into (5)-2-methylbutanal (82% ee). 

Pt(II) complexes generally give hydroformylation products with higher asymmetric induction than Rh(I) complexes. A Pt(II)-SnCl2 complex with a chiral phosphine, aminophosphine, or phosphinite also catalyzes the hydroformylation of styrene in up to 86% optical yield (115). Stille noticed that the PtCl2(bppm)-SnCl2 combined catalyst is... 

New inq)etus for asymmetric hydroformylations came primarily from Takayas phosphine-phosphinite ligand (BINAPO) 4 which constitutes an enormous breakthrough l In combination with rhodium the BINAPO ligand gave enantioselectivities up to 95% and i/n ratios > 86/14 in the hydroformylation of substituted styrene derivatives. Conversions are > 99% at substrate/catalyst ratios between 300 and 2000. Shortly afterwards, similar catalytic results were reported by Union Carbide with chiral diphosphinite ligands, e.g. 5 . After many years of stagnation these new catalysts now point the way towards fixture developments in asymmetric hydroformylation. 

Roucoux, A., Agboussou, F., Mortreux, A. and Petit, F. (1993) New alky-larylamido phosphine phosphinites as chiral diphosphines for asymmetric hydrogenation of acilated keto compounds. Tetrahedron Asymm. 4,2279-... 

Chiral phosphines are widely used as auxiliaries for various metal-catalyzed asymmetric reactions and can be prepared from stable phosphine-borane complexes. Secondary P-chiral phos-phine-boranes can be prepared by reductive lithiation of the corresponding tertiary phosphine-borane using LN (eq Likewise, P-chiral tertiary phosphine ligands can be produced by the reductive lithiation of phosphinite-boranes followed by alkylation, both proceeding with retention of configuration (eq 18). ... 

The transformation of readily available enantiopure //-menthylphosphinates 2 into chiral phosphinous acid boranes 5 permits the elaboration of bulky P-stereogenic secondary phosphine boranes. Taking advantage of the synthetic potential of these compounds, abroad range of hindered P-chiral tertiary phosphine boranes 6 were prepared with excellent enantiomeric excesses [12,13]. Phosphinous acid 5 can easily be converted into one or the other enantiomer of the secondary phosphines boranes (Sp)- or (/ p)-6 by stereoselective reduction or substitution of the phosphinite borane derivatives, respectively (Scheme 4 and Table 1). 

Modification of the well known diop-Rh catalyst by the inclusion of o-methoxy-groups on the phenyl substituents results in a reversal of the R S ratio in the amino-acid products, relative to diop itself. Overall enantiomeric enrichments are comparable with those obtained with diop-Rh It has been shown that in some cases, chiral Rh -phosphinite complexes derived from sugars are more effective in asymmetric hydrogenations than the corresponding phosphine complexes. ... 

Example 4.8 Synthesis of P-Chiral Phosphines from a Borane-Protected Phosphinite [ 14]. 

Nozaki K, Li WG, Horiuchi T, Takaya H Saito T, Yoshida A, Matsumura K, Kato Y, Imai T, Miura T, Kumobayashi H. A new StereocontroUed approach to 1 beta-methylcarbapenem asymmetric hydroformylation of 4-vinyl beta-lactams catalyzed by Rh(I) complexes of chiral phosphine-phosphites and phosphine-phosphinites. J. Org. Chem. 1996 61 7658 7659. 

Figure 7.1. Chiral diphosphine, diphosphite, phosphine-phosphite, phosphine-phosphinite, amine-phosphinite, and polymer-anchored ligands used for asymmetric hydroformyiatioD.

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