(2R,3R)-(-)-2,3-Bis(diphenylphosphino)bicyclo[2.2.1]hept-5-ene

Asymmetric hydrogenation with rhodium catalyst

Typical procedure: (2R,3R)-(-)-Norphos (3.7 mg) and [Rh(cod)Cl]2 (4 mg) were stirred in methanol (5 mL) in a hydrogen atmosphere for 15 min, giving an orange solution. (Z)-2-Benzamido-3-ferrocenylacrylic acid (1)(3.76 g) was dissolved in methanol (20 mL) and the catalytic orange solution was added under nitrogen. Then, the reaction vessel was vented three times with hydrogen. Hydrogenation at 1.1 atm proceeded at room temperature and was stopped after 3.5 d, when the hydrogen uptake was complete. After the hydrogenation, the solvent was evaporated and the residue was treated with 1N NaOH (2.5 mL) for 30 min. The solution was filtered, diluted with water (20 mL), acidified with 1N HCl and extracted with ether. The organic phase was dried over Na2SO4 and concentrated to dryness to give (2S)-2-benzamido-3-ferrocenylpropanic acid (2)(3.4 g, 90 %, 90.5-94.5 % ee) as yellow solid.

• H. Brunner, W. König, B. Nuber, Tetrahedron: Asymmetry 1993, 4, 699.