[20300-53-7]  · C12H28P2  · (234.30)

(a chiral ligand for transition metal-catalyzed asymmetric reactions)

Alternate Name: BisP*.

Physical Data: mp 23.5-25.5 °C.

Solubility: soluble in most organic solvents.

Form Supplied in: borane complex of 1 is commercially available as colorless crystals.

Preparative Methods: phosphorus trichloride is allowed to react sequentially with alkylmagnesium chloride, methylmagnesium bromide, and BH3-THF complex in THF to give alkyldimethylphosphine-borane (eq 1).1 The phosphine-borane so obtained is enantioselectively deprotonated by s-BuLi in the presence of (-)-sparteine in Et2O at -78 °C to -50 °C, followed by oxidative coupling using CuCl2 to give a BisP*-borane complex. Recrystallization from toluene affords enantiomerically pure product. The boranato group is removed by the reaction with trifluoromethanesulfonic acid in toluene, followed by treatment with aqueous KOH.

Purification: filtered through Al2O3 with Et2O elution under N2 or Ar atmosphere.

Handling, Storage, and Precautions: stench. Undergoes oxidation to the phosphine oxide on standing in air. Usually prepared before use by deboranation of the air stable phosphine-borane.

Rhodium-Catalyzed Asymmetric Hydrogenation of Olefins

A rhodium complex of BisP* (1) is a highly effective catalyst for asymmetric hydrogenation of some olefinic compounds.1 BisP*-rhodium complex 2 is prepared from 1 and [Rh(nbd)2]BF4 in THF (eq 2). The hydrogenation of a-(acylamino)-acrylic derivatives are carried out at room temperature and an initial H2 pressure of 2 or 6 atm in the presence of the catalyst (0.2 mol%). The reactions proceed rapidly and are complete within 0.2-2 h to afford a-amino acid derivatives with enantioselectivity of up to 99.9% (eq 3). This methodology can also be applicable to b-unsubstituted and b,b-disubstituted a-(acylamino)acrylates. The excellent enantioselectivities are again observed in hydrogenation of itaconic acids,2 enamides,3 and dehydro-b-amino acids4 (eq 4-6).

Ruthenium-Catalyzed Asymmetric Hydrogenation of b-Keto Esters

A ruthenium complex of 1 catalyzes enantioselective hydrogenation of b-keto esters.5 The 1-Ru complex is prepared by reacting 1 with (COD)Ru(2-methylallyl)2, followed by treatment with methanolic HBr in acetone.6 The hydrogenations are carried out at 50-70 °C and an initial H2 pressure of 6 atm in the presence of the 1-RuBr2 complex (0.13-1.4 mol %). Various types of b-keto esters and related substrates are hydrogenated to afford b-hydroxy esters in high yield and with excellent enantioselectivity (eq 7). In the case of a-keto esters, slightly lower enantioselectivity is observed, and g-keto esters are not subjected to hydrogenation under the conditions.

Related Reagents.


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Hiroshi Danjo & Tsuneo Imamoto

Chiba University, Chiba, Japan

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.