Asymmetric oxidation of 2-(arylsulfenyl)pyrroles
The asymmetric oxidation of prochiral 2-(arylsulfenyl)pyrroles has been investigated. A marked electronic effect within the substrate significantly influenced the degree of enantioselectivity obtai...
Asymmetric synthesis. Metal complex mediated synthesis of chiral glycine by enantioselective proton exchange
On etudie l'echange selectif des protons methylenes d'un coordinat glycine coordine. On montre aussi que la vitesse de l'echange peut etre employee pour produire de la glycine chirale a n'importe quel degre de purete chirale. Le systeme choisi est [Co((S,S)-proam)(picgly)] + un complexe de Co(III) contenant 2 coordinats tridentes dont l'un contient un reste glycine (proam=iminodimethylene-2,2' bis-pyrrolidine; picgly=N-picolinoylglycine)
FLUOROUS BIPHASIC OXIDATION OF SULFIDES CATALYSED BY (SALEN)MANGANESE(III) COMPLEXES
Abstract Quadridentate Schiff base ligands derived from 1,2-diamines and fluorous derivatives of salicylaldehyde were prepared and the corresponding manganese(III) complexes were tested as catalysts in the selective oxidation of alkyl aryl sulfides with PhIO. Complexes bearing two fluorinated ponytails were soluble in standard organic solvents and were used under classical homogeneous conditions, whereas heavily fluorinated complexes could be used in a CH3CN/perfluorooctane biphasic system. In both cases, sulfoxides were obtained as the main products, together with variable amounts of sulfones (≤10%), depending on the nature of the substrate and the catalyst. When reactions were carried out under fluorous biphasic (FB) conditions, the selectivity for sulfoxides was improved and the catalyst could be easily recovered by simple phase separation and reused up to four times. Despite their good chemoselectivity, catalytic efficiency and recyclability, chiral fluorous (salen)manganese(III) complexes showed low enantioselectivities in preliminary experiments run under fluorous biphasic conditions.