O-unprotected aldoses (D-glucose, D-galactose and D-mannose) and D-fructose in THF or 1,4-dioxane using anhydrous FeCl3 as promoter afforded either aldofuranosides 1, 3, 4 in good overall yields or exclusively β-D-fructopyranosides 7. Conversely α-D-aldopyranosides 2, 5 and 6 were obtained respectively from D-glucose, D-mannose and N-acetyl-D-glucosamine when the reactions were performed in the presence
O-Glycosylation of a variety of long chain alcohols with totally unprotected uronic acids (D-glucuronic and D-galacturonic acids) and neutral carbohydrates (D-glucose, D-galactose, D-mannose and D-glucofuranurono-6,3-lactone), performed in heterogeneous media and promoted by Lewis acids (ferric chloride or boron trifluoride diethyl etherate), afforded alkyl D-glycofuranosiduronic acids and alkyl D-glycofuranosides, respectively, in high yields. Both chemoselectivity and anomeric stereoselectivity were enhanced by complexing agents, i.e. calcium or barium chloride. (C) 1998 Elsevier Science Ltd. All rights reserved
Boronic Acids as Phase-Transfer Reagents for Fischer Glycosidations in Low-Polarity Solvents
作者:Sanjay Manhas、Mark S. Taylor
DOI:10.1021/acs.joc.7b01880
日期:2017.11.3
Protocols employing phenylboronic acid as a phase-transfer reagent for Fischer glycosidations in low-polarity organic solvents are described. In addition to providing rate acceleration, the formation of a substrate-derived boronic ester alters the course of the reaction by selective promotion of a furanoside- or pyranoside-selective pathway. Computational modeling of the relative energies of the glycoside-derived