In rhodium(I)-catalyzed asymmetric hydrogenations of electron deficient olefins, the electron-rich and sterically encumbered phosphine ligand, MOD-BDPMI, exhibited higher enantioselectivities than BDPMI ligands. Moreover, the N-substituents of the imidazolidin-2-one backbone affected the enantioselectivity. Thus, using the N,N′-dimethylated MOD-BDPMI ligand 2b, (Z)-α-(N-acetamido)cinnamic acid 3 was hydrogenated with 100% conversion to give the saturated α-amino acid with ee of 88.7%.
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We are grateful for financial support from the Ministry of Science and Technology (National Research Laboratory Program, 2N22890), from KIST (2E17512) and CMDS at KAIST.