Radical β-elimination of vicinal phenylselenide and xanthate azides in sugar derivatives

Safe and Scalable Continuous Flow Azidophenylselenylation of Galactal to Prepare Galactosamine Building Blocks

“…The use of silica filtration prior to evaporation therefore does not introduce an extra step to the preparative protocol, but simply exchanges the order between silica filtration and solvent evaporation. Presumably, selenoglycosides 2 – 3 are converted into 6 – 8 via radical-mediated homolytic cleavage of the C–Se anomeric bond or β-elimination to afford galactal 1 as an intermediate. ,, Alternatively, oxidation of the phenylselenyl group to the corresponding selenone would afford a good leaving group, rendering C1 susceptible to nucleophilic attack . Involvement of BAIB on the formation of 6 – 8 under reduced pressure resulting from incomplete reduction in the aqueous quenching was ruled out, as no BAIB signals were observed during 1 H NMR analysis.…”

Carbanionic Reactivity of the Anomeric Center in Carbohydrates

“…As the last review on glycals 37 is 20 years old, it may be useful to list methods of preparation for these substances which, starting from monosaccharide derivatives, utilize reactions involving no anomeric carbanions as intermediates. Radical-induced eliminations were achieved from 1-thioglycoside-2-xanthates, , 2-azido-2-deoxy-selenoglycosides, a 2-phosphonooxy-1-thioglucoside, a 1,2- O -thiocarbonyl-α- d -glucose derivative, and a C -(1,2-dibromo-1,2-dideoxy- d -glucopyranosyl)formate . A C-2 radical or anion may be the intermediate in the transformation of 1,6-anhydrohexopyranose derivatives into glycals .…”

Radical-Mediated Synthesis of α-C-Glycosides Based on N-Acyl Galactosamine

“…Addition of N 3 • to d -galactal is postulated 14 to proceed via the 2-azido anomeric radical 8 , but to date all attempts to trap this intermediate with methyl acrylate have failed. Only d -galactal was recovered …”