mediated alkynylation reaction was studied for the preparation of C-glycosides from unactivated alkynes. Different glycosyl donors such as glycals and anomeric acetates were tested towards an alkynyl zinc reagent obtained from alkynes using zinc dust and ethyl bromoacetate as an additive. The method provides simple, mild and stereoselectiveaccess to alkynyl glycosides both from aromatic and aliphatic acetylenes
A diastereoselective, metal-free, one-pot domino synthetic strategy was developed for the transformation of glycals into new chiral scaffolds. Optimization of the reaction conditions to exclude normal Ferrier products, characterization of the new entities, and a plausible mechanism were investigated.
A highly stereoselective rapid C-glycosylation reaction has been developed between glycal and unactivated alkynes in the presence of coppertriflate and ascorbic acid at low catalyst loading and at room temperature. A wide variety of glycals and aryl acetylenes participate in the reaction smoothly. TfOH generated during the reduction of Cu(OTf)2 by ascorbic acid may be the active catalyst for the glycosylation.
Nucleophilic Addition of Potassium Alkynyltrifluoroborates to <scp>d</scp>-Glucal Mediated by BF<sub>3</sub>·OEt<sub>2</sub>: Highly Stereoselective Synthesis of α-<i>C</i>-glycosides
作者:Adriano S. Vieira、Pedro F. Fiorante、Thomas L. S. Hough、Fernando P. Ferreira、Diogo S. Lüdtke、Hélio A. Stefani
DOI:10.1021/ol8022177
日期:2008.11.20
A convenient, mild and highly stereoselective method for C-glycosidation (alkynylation) of D-glucal with various potassium alkynyltrifluoroborates, mediated by BF3 center dot OEt2 and involving oxonium intermediates, preferentially provides the alpha-acetylene glycoside products with good yields.