2,5-Dimethyl-3,4-bis[(2R,5R)-2,5-dimethylphospholano]thiophene: first member of the hetero-DUPHOS family

The 2,5-dimethyl-3,4-bis[(2R,5R)-2,5-dimethylphospholano]thiophene (UlluPHOS), a new thiophene-based analogue of (R,R)-1,2-bis(phospholano)benzene (Me-DuPHOS), was synthesized, geometrically and electronically characterized, and employed as ligand of Rh and Ru in some standard hydrogenation reactions of prostereogenic functionalized carbon−carbon and carbon−oxygen double bonds. The synthesis of UlluPHOS is much easier than that provided for Me-DuPHOS. UlluPHOS and Me-DuPHOS display very similar geometries, while the electronic availability of the former is higher than that exhibited by the latter. The Rh and Ru complexes of UlluPHOS produced excellent enantiomeric excesses (98.9−99.5%) in the hydrogenation of N-acetyl-α-enamino acids and reaction rates higher than those found when employing the analogous complexes of Me-DuPHOS.