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Three inexpensive oxidation reagents, namely pyridinium chlorochromate, chromium trioxide-dipyridine and nicotinium dichromate were utilized for oxidation of carbohydrates in 78-92% yield. Hydration could be eliminated in the oxidation of pentopyranosides and hexopyranosides, while pentofuranosides had a tendency to be easily hydrated during the oxidation. In the carbon-13 n.m.r. study, the carbonyl function resulted from the oxidation affected on the chemical shifts of alpha- and beta -carbons of methyl 3,4-O-isopropylidene- beta-D-arabinopyranosid-2-ulose (8) and 1, 2 : 4, 5-di-O-isopropylidene-beta-D-erythro-2, 3-hexodiulo-2, 6-pyranose (10) to slightly down fields (0.7-2.6 p.p.m.) compared with the chemical shifts before oxidation. While the carbonyl groups of 1,2-O-isopropylidene-5-O-ethyloxycarbonyl-alpha-D-erythro-pentofuran-3-ulose (4) and methyl 3,5-O-isopropylidene-alpha-D-threo-pentofuranosid-2-ulose (6) pushed the alpha-carbons to up fields (3.2-18.3 p.p.m.). However, the order of signals on the spectra before and after oxidation remained unaltered.
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