Other Mixed-Donor Bidentate Ligands

Borner reported the synthesis of pyrophosphites 149 with chiral binaphthyl substituents [118]. The results showed that the Hg-binaphthyl unit was the best for the Rh-catalyzed hydrogenation of methyl (Z)-2-acetamidocinnamate (48% ee) and dimethyl itaconate (70% ee). 

In 1982, Yamashita reported the application of L-talopyranoside-based phos-phine-phosphinite ligand 165 (Fig. 27.15), and found that it induced low enan-tioselectivity (4.7-13% ee) in the hydrogenation of a-acetamidocinnamic acid [119]. Reetz introduced the phosphine-phosphonite ligand (151-153), which led to moderate enantioselectivity (52-88% ee) in the Rh-catalyzed hydrogenation of dimethyl itaconate [120]. The binaphthyl unit remained an essential element in the system. 

Pizzano and Suarez described a convenient preparation of a series of new chiral phosphine-phosphites based on the easy demethylation of o-anisyl phosphines [124]. Rh-156a complex was found to be the most effective catalyst for the hydrogenation of dimethyl itaconate (99.6% ee), whereas 155b and 156a induced 99% ee in the hydrogenation of methyl N-2-acetamidocinnamate. Reetz 

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