New Effective Transformations of Monosaccharides by Selective Inversion

摘要: Regio- and stereoselective acetalizations of methyl α-D-lyxopyranoside (1), β-L-arabinopyranoside (6), α-D-galactopyranoside (11), β-D-galactopyranoside (13) with chloral, including an inversion the configuration at C-3, were achieved dicyclohexylcarbodiimide as a coagent. Additionally, formed 3,4-O-(2,2,2-trichloroethylidene)-α-D-arabinopyranoside 2, 2,3-O-(2,2,2-trichloroethylidene)-β-L-lyxopyranoside 7, 2,3-O-(2,2,2-trichloroethylidene)-α-D-gulopyranoside 12, 2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranosides 14 15 contain N-cyclohexylcarbamoyl group vicinal to chloral acetal moiety; compounds 12 15, moreover, formyl in 6-position. The carbamoyl functions may be cleaved stepwise methanolic sodium methoxide. Deformylation 6-O-formyl derivative affords urethane 16 simultaneous migration from 4- fluorination 3 8 anhydrous hydrogen fluoride/nitromethane/acetic anhydride, giving glycosyl fluorides 4 9 without any cleavage cyclic functions, is described. BF3-catalyzed glycosylations chloro-ethanol 9α/β yield α-glycoside 5 anomeric mixture 10α/β, respectively, showing that neither function 3,4-O-nor 2,3-O-position affects such reactions.