Hydrogenation of Dehydro-a-Amino Acids and Enamides

Catalyst 12c recycled seven times on the hydrogenation of 13a (R = H) with 99% conversion and 95.0-89.5% ee. 

as evidenced by the inactivity of the supernatant and lack of metal leaching ( 1 ppm) in both the filtered solution and isolated product. 

The reusability of the catalyst system was also examined in the hydrogenation of (Z)-methyl 2-acetamidobut-2-enoate. Using the filtration-recovered catalyst, the hydrogenation proceeded with near-quantitative conversion and constant enantioselectivity (96-92% ee) for at least 10 cycles and with a standard reaction time of 20 h. The reaction profile of the hydrogenation showed that the catalyst reactivity declined with consecutive runs, presumably due to partial catalyst decomposition during catalyst recovery. 

---