Benzylidene Acetal Fragmentation Route to 6-Deoxy Sugars: Direct Reductive Cleavage in the Presence of Ether Protecting Groups, Permitting the Efficient, Highly Stereocontrolled Synthesis of β-<scp>d</scp>-Rhamnosides from <scp>d</scp>-Mannosyl Glycosyl Donors. Total Synthesis of α-<scp>d</scp>-Gal-(1→3)-α-<scp>d</scp>-Rha-(1→3)- β-<scp>d</scp>-Rha-(1→4)-β-<scp>d</scp>-Glu-OMe, the Repeating Unit of the Antigenic Lipopolysaccharide from <i>Escherichia</i> <i>h</i><i>ermannii</i> ATCC 33650 and 33652
作者:David Crich、Qingjia Yao
DOI:10.1021/ja048070j
日期:2004.7.1
donors bearing a carboxylated donor on O3 is a highly alpha-selective mannosyl and, after radicalfragmentation, alpha-d-rhamnosyl donor. Using this stereoselective glycosylation/radical-fragmentation approach, a concise synthesis of the title tetrasaccharide is realized in which both the beta-d- and alpha-d-rhamnopyranosyl units are obtained in a single step by a double radicalfragmentation of the modified
We have developed a highlyenantioselective aza-Henry reaction of aryl α-ketoester-derived N-Ts ketimines with a wide range of substrate scope by a simpler bifunctional thiourea-tertiary amine catalyst derived from quinine. A variety of ketimines were investigated and corresponding products were obtained in excellent yields (up to 99% yield) with excellent enatioselectivities (up to 99% ee).
N-p-tolylsulfonyl-2-arylglycinates in high yields by a combination of aluminum(III) chloride and diphenylsilane under operating conditions in which diphenylsilane was added to the pre-formed substrate-aluminum(III) chloride complex in dichloromethane and the mixture stirred. The case of an exactly equivalent amount of aluminum(III) chloride as the substrate resulted in good results.
The 4,6-<i>O</i>-[α-(2-(2- Iodophenyl)ethylthiocarbonyl)benzylidene] Protecting Group: Stereoselective Glycosylation, Reductive Radical Fragmentation, and Synthesis of β-<scp>d</scp>-Rhamnopyranosides and Other Deoxy Sugars
作者:David Crich、Qingjia Yao
DOI:10.1021/ol034741r
日期:2003.6.1
[reaction: see text] In the thioglycoside/BSP/Tf(2)O glycosylation method, the 4,6-O-[alpha-(2-(2-iodophenyl)ethylthiocarbonyl)benzylidene] group enforces beta-selectivity in mannopyranosylations. Following glycosylation, treatment with Bu(3)SnH in toluene at reflux affords regioselective, reductive fragmentation to the 6-deoxy-beta-mannosides (beta-rhamnosides). Applied to glucosides, the radical fragmentation
Facile Preparation of the Methyl Acetal of Methyl Phenylglyoxylate
作者:Pakorn Bovonsombat、Edward McNelis
DOI:10.1080/00397919208019092
日期:1992.8
Abstract The methyl acetal of methyl phenylglyoxylate has been prepared from halophenylethynes, N-iodosuccinimide and catalytic amounts of (hydroxy(p-tosyloxy)iodo)benzene or p-toluenesulfcnic acid in methanol at room temperature.