BINAP ligand, Noyori catalytic

The discovery by the recent Nobel-laureate, Ryoji Noyori, of asymmetric hydrogenation of simple ketones to alcohols catalyzed by raras-RuCl2[(S)-binap][(S,S)-dpen] (binap = [l,l -binaphthalene-2,2/-diyl-bis(diphenylphosphane)] dpen = diphenylethylenediamine) is remarkable in several respects (91). The reaction is quantitative within hours, gives enantiomeric excesses (ee) up to 99%, shows high chemoselecti-vity for carbonyl over olefin reduction, and the substrate-to-catalyst ratio is >100,000. Moreover, the non-classical metal-ligand bifunctional catalytic cycle is mechanistically novel and involves heterolytic... 

It is certain that many more applications of catalytic asymmetric intramolecular Mizoroki-Heck reactions will be described in the future. This survey makes apparent the small number of ligands that have been used thus far, with Noyori and coworkers BINAP ligand being the most widely employed [80]. Two future trends are easy to predict a larger variety of chiral ligands [56, 58, 81, 82] will be used in asymmetric Mizoroki-Heck processes and a greater variety of cascade processes involving intramolecular Mizoroki-Heck reactions will be developed. 

The principles of directed and asynunetric reactions were first developed for hydrogenation, as discussed in Section 9.2. Asymmetric hydrosilation of ketones can now be carried out catalytically with rhodium complexes of diop (9.22). The widely used chiral ligand Et-duPHOS, made by Burk at du Pont, allows chiral amination of ketones via Eq. 14.50. Note how the use of the hydrazone generates an amide carbonyl to act as a ligand, as is known to favor high e.e. (see Section 9.2). Noyori s powerful BINAP ligand has been applied to a very large number of asymmetric reactions. 

A later paper by workers associated with the Takasago process reported on ab initio MO calculations for the catalytic cycle. Their work suggested that steps b and c (Scheme 9.22) involved an intramolecular OA of C-H, followed by a RE in which the hydride ligand attached itself to the terminal carbon of the allyl group. See M. Yamakawa and R. Noyori, Organometallics, 1992, 11, 3167. It is not clear which pathway is correct because the theoretical study used only PH3 and not BINAP to model the Rh-catalyzed isomerization. See also C. Chapuis, M. Barthe, and J.-Y. de Saint Laumer, Helv. Chim. Acta, 2001, 84, 230. 

The first place in catalytic hydrogenation nowadays is taken by Rh or Ru complexes of BINAP. This ligand has axial chirality as the naphthalene rings cannot rotate past each other. These compounds were developed by Noyori, who with Knowles and Sharpless received the 2001 Nobel prize for their contributions to asymmetric synthesis. BINAP 20 is usually made from BINOL 19 and either 19 or 20 can be resolved. Rhodium complexes similar to those we have met include a molecule of cyclooctadiene and, as these are Rh(I) compounds, a counterion, often triflate 21. Both enantiomers of BINAP are available commercially.8... 

Homogeneous catalytic asymmetric hydrogenation has become one of the most efficient methods for the synthesis of chiral alcohols, amines, a and (3-amino acids, and many other important chiral intermediates. Specifically, catalytic asymmetric hydrogenation methods developed by Professor Ryoji Noyori are highly selective and efficient processes for the preparation of a wide variety of chiral alcohols and chiral a-amino acids.3 The transformation utilizes molecular hydrogen, BINAP (2,2 -bis(diphenylphosphino)-l,l -binaphthyl) ligand and ruthenium(II) or rhodium(I) transition metal to reduce prochiral ketones 1 or olefins 2 to their corresponding alcohols 3 or alkanes 4, respectively.4... 

Example 9.2 The industrial method for large-scale production of both enantiomers of menthol is based on an asymmetric catalytic reaction in the key step promoted by the Rh(II) complex of the well-known chiral ligand BINAP, available in both enantiomeric forms. This process was developed by Takasago Research Institute, Tokyo, in collaboration with Nobel laureate R. Noyori (Scheme 9.2) [9]. 

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