Reactions of several monosaccharide-derived alcohols with p-acetamidobenzenesulfonyl azide and DBU

Attempted diazo transfer to 1-O-(2-phenylacetyl)-2,3;5,6-di-O-isopropylidene-α-d-mannofuranose using p-acetamidobenzenesulfonyl azide (p-ABSA) and DBU as base affords 1-O-(2-diazo-2-phenylacetyl)-2,3;5,6-di-O-isopropylidene-α-d-mannofuranose in low yield along with 2,3;5,6-di-O-isopropylidene-α-d-mannofuranose, 1-azido-2,3;5,6-di-O-isopropylidene-β-d-mannofuranose, as well as the unreacted starting material. The azido sugar likely arises from α-mannofuranosyl sulfonate ester formation, through displacement of azide from p-ABSA by the sugar lactol, followed by stereospecific displacement by azide anion on the furanosyl sulfonate ester. This outcome has been studied further with the conditions being applied to several common monosaccharide derivatives. Accessible substrates afford the azido sugar in an overall one-pot alcohol-to-azide conversion, while hindered substrates yield the sulfonate esters.