Generation and cycloaddition reactions of pyranose-1-carbonitrile oxides

Stannate(II) reduction of the β-d-glucopyranosylnitromethane derivative 4 affords aldoxime 5, which provides access to the nitrile oxide 7, either on treatment with aq. hypochlorite, or via conversion to the hydroximoyl chloride 11 followed by base-mediated dehydrohalogenation. d-Galactose-, d-mannose- and d-xylose-derived nitrile oxides are generated similarly. The nitrile oxides either dimerise to 3,4-dipyranosyl-1,2,5-oxadiazole N-oxides or are trapped as cycloadducts in the presence of dipolarophiles.