Stereoselective synthesis of chiral sulfilimines from N-mesyloxycarbamates: metal-nitrenes versus metal-nitrenoids species.
The synthesis of a variety of chiral sulfilimines and sulfoximines is described. The amination of thioethers with a chiral N-mesyloxycarbamate was achieved in high yields and stereoselectivities using Rh2[(S)-nttl]4 as catalyst in the presence of 4-dimethylaminopyridine (DMAP) and a pyridinium salt, such as bis(DMAP)CH2Cl2 or a viologen salt. These additives proved instrumental to enhance both the yield and the stereochemical discrimination of the reaction. Mechanistic studies and control experiments have elucidated the role of these additives. DMAP served as an apical ligand for the rhodium catalyst: an X-ray crystal structure of the (DMAP)2·[Rh2{(S)-nttl}4] complex was obtained. This complex displayed a lower and irreversible redox potential. Control experiments with preformed Rh(II)-Rh(III) complex suggested such a catalytically active species in the thioether amination process. Diastereoselectivities were influenced by the sulfonyloxy leaving group, ruling out the possibility of a common metal nitrene species and instead suggesting a rhodium-nitrenoid complex. It is believed that the bispyridinium salt played the role of a phase transfer catalyst, influencing both the yield and the diastereoselectivity of the reaction.
Département de Chimie, Center for Green Chemistry and Catalysis, Université de Montréal, C.P. 6128, Succursale Centre-ville, Montréal, Québec, Canada H3C 3J7.
Hélène
H
Lebel
Département de Chimie, Center for Green Chemistry and Catalysis, Université de Montréal, C.P. 6128, Succursale Centre-ville, Montréal, Québec, Canada H3C 3J7.
Henri
H
Piras
D015761:4-Aminopyridine / Q000031:analogs & derivatives* / Q000737:chemistry; D000586:Amination; D002384:Catalysis; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007097:Imines / Q000138:chemical synthesis* / Q000737:chemistry*; D008024:Ligands; D008670:Metals / Q000737:chemistry*; D015394:Molecular Structure; D011726:Pyridinium Compounds / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry*; D013237:Stereoisomerism
D056831:Coordination Complexes; D007097:Imines; D008024:Ligands; D008670:Metals; D011726:Pyridinium Compounds; C586946:sulfilimine; C017621:phenylnitrene; D015761:4-Aminopyridine; D012238:Rhodium; C003885:4-dimethylaminopyridine