α-Halogenoacetanilides as hydrogen-bonding organocatalysts that activate carbonyl bonds: Fluorine versus chlorine and bromine
α-Halogenoacetanilides (X=F, Cl, Br) were examined as H-bonding organocatalysts designed for the double activation of Ci£O bonds through NH and CH donor groups. Depending on the halide substituents, the double H-bond involved a nonconventional Ci-H×××O in
N-aryl-O-glycosyl haloacetimidates as glycosyl donors
Reaction of 1-O-unprotected tetra-O-acetyl- and tetra-O-benzyl- glucopyranose with N-aryl haloacetimidoyl chlorides in the presence of sodium hydride and 15-crown-5 afforded N-aryl-O-glucopyranosyl haloacetimidates. Mainly the β-anomers were obtained in this anomeric O-acylation-type reaction. The glycosyl donor properties of these haloacetimidates were investigated with 6-O- and 4-O-unprotected glucopyranosides as acceptors. The results were compared with those obtained with the corresponding O-glucopyranosyl trichloroacetimidates as glycosyl donors and the same acceptors. It was found that N-(2-chloro-6-methylphenyl)-O-glucopyranosyl trifluoroacetimidates (16Ad, 16Bd) exhibit glycosyl donor properties closely related to those of the corresponding N-unsubstituted O-glucopyranosyl trichloroacetimidates (12A, 12B). Copyright Taylor & Francis Group, LLC.
Huchel, Uschi,Tiwari, Pallavi,Schmidt, Richard R.
experimental part
p. 61 - 75
(2011/07/06)
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