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Electronic effects on the regio‐ and enantioselectivity of the asymmetric aminohydroxylation of O ‐Substituted 4‐Hydroxy‐2‐butenoates
Author(s) -
Chuang ChihYuan,
Vassar Victor C.,
Ma Zuping,
Geney Raphaël,
Ojima Iwao
Publication year - 2002
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.10050
Subject(s) - chemistry , substituent , moiety , electronic effect , stereochemistry , regioselectivity , substrate (aquarium) , ligand (biochemistry) , medicinal chemistry , catalysis , organic chemistry , steric effects , biochemistry , oceanography , receptor , geology
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. Chirality 14:151–162, 2002 . © 2002 Wiley‐Liss, Inc.