Electronic effects on the regio- and enantioselectivity of the asymmetric aminohydroxylation of O-substituted 4-hydroxy-2-butenoates.
Regio- and enantioselectivity in the asymmetric aminohydroxylation (AA) reaction of O-substituted 4-hydroxy-2-butenoates as well as the mechanism of the reaction were studied. When the electronic properties of the phenyl group in a substrate were altered by using different substituents, two conflicting trends were observed: The O-benzoyl substrates showed greater regio- and enantioselectivity when an electron-donating substituent was attached at the C-4 position of the phenyl group, while the O-benzyl substrates exhibited better regio- and enantioselectivity with an electron-withdrawing substituent at the C-4 position of the phenyl moiety. Thus, these results have disclosed hitherto unknown remarkable electronic effects in the AA reaction. Detailed analysis of possible electronic interactions in the chiral catalyst-substrate complex has revealed the importance of dipolar aromatic-aromatic interactions between the aromatic substituent of the substrate and the nitrogen heteroaromatic moiety of the chiral ligand for effective regiocontrol as well as enantioface selection in the AA reaction. A plausible model of the key intermediate in the AA reaction of O-substituted 4-hydroxy-2-butenoates is proposed.
Chuang
Chih-Yuan
CY
Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York, USA.
Vassar
Victor C
VC
Ma
Zuping
Z
Geney
Raphaël
R
Ojima
Iwao
I
D000586:Amination; D002087:Butyrates / Q000138:chemical synthesis*; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D006863:Hydrogen-Ion Concentration; D006900:Hydroxylation; D007202:Indicators and Reagents; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D013055:Spectrophotometry, Infrared; D013237:Stereoisomerism
D002087:Butyrates; D007202:Indicators and Reagents; D008024:Ligands