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 analog 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 std. hydrogenation reactions of pro-stereogenic 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. Rh and Ru complexes of UlluPHOS produced excellent enantiomeric excesses (98.9-99.5%) in the hydrogenation of N-acetyl-a-enamino acids and reaction rates higher than those found when employing the analogous complexes of Me-DuPHOS.