Stereoselective synthesis of 5,5-dimethyl-2-oxo-2-(3,4,6-tri-O-acetyl-2-deoxy-α-<scp>D</scp>-hexopyranosylseleno)-1,3,2-dioxaphosphorinane: novel observations on the selenono–selenolo isomerization of phosphoroselenoates

Abstract

The first example of a 1-phosphoroselenoate of a 2-deoxy sugar has been obtained by three independent routes: (A) selenophosphorylation of 3,4,6-tri-O-acetyl-2-deoxy-D-arabino-hexopyranose (4) with selenophosphorochloridate (5) followed by selenono–selenolo isomerization; (B) condensation of 3,4,6-tri-O-acetyl-2-deoxy-α-D-arabino-hexopyranosyl bromide (8) with O,O-dialkylphosphoroselenoate (9), and (C) addition of O,O-dialkylphosphoroselenoic acid (11) to 3,4,6-tri-O-acetyl-D-glucal (1). All these reactions proceed with high yield and full stereoselectivity to afford the α-selenophosphate of 2-deoxy-D-arabino-hexopyranose (7). It has been shown that the selenono–selenolo isomerization (6)→(7) which occurs in route (A) proceeds via the intermediate 2-deoxyglycosyl chloride (12). This finding confirms the mechanism proposed by Chabrier et al. for the selenono–selenolo phosphate Isomerization catalyzed by ammonium halides.