Regioselective Benzoylation of 4,6-O-Benzylidene Acetals of Glycopyranosides in the Presence of Transition Metals
摘要:
Benzoylation of 4,6-O-benzylidene acetals of glycopyranosides by benzoic anhydride in acetonitrile in the presence of Cu(CF3COO)(2) as a promoter gave 2-benzoates for alpha-D-glucopyranosides and alpha-D-mannopyranosides and 3-benzoates for beta-D-galactopyranosides in good yields with high regioselectivity. Benzoylation of 4,6-O-benzylidene acetals of glycopyranosides of D-galactose and D-mannose by benzoyl chloride in the presence of MoO2(acac)(2) as a catalyst in all studied cases led to regioselective 3-O-substitution.
Regio- and chemoselective reductive cleavage of 4,6-O-benzylidene-type acetals of hexopyranosides using BH3·THF–TMSOTf
作者:Katalin Daragics、Péter Fügedi
DOI:10.1016/j.tetlet.2009.03.194
日期:2009.6
cyclic acetals of carbohydrates undergo efficient reductive ring opening using BH3·THF and a catalytic amount of TMSOTf at room temperature. 4,6-O-Benzylidene-hexopyranosides afford the corresponding 4-O-benzyl ethers exclusively, in high yields. Other benzylidene-type acetals, such as naphthylmethylene and 4-methoxybenzylidene acetals are also cleaved with the same reagent. The conversions are highly regio-