A reinvestigation of the structures for 5-diazouracil, 5-diazouridine, 5-diazo-2′-deoxyuridine and certain related derivatives by proton magnetic resonance spectroscopy

The structure of 5-diazouracil and several closely related derivatives have been revised on the basis of pmr spectroscopy. 5-Diazouracil, 5-diazouracil hydrate, 5-diazouracil methanol adduct, 5-diazouridine and 5-diazo-2′-deoxyuridine have been reassigned the structures 5-diazopyrimidin-2,4(3H)dione (XI), 5-diazo-6-hydroxy-1,6-dihydropyrimidin-2,4(1H,3H,6H)dione (XIII), 5-diazo-6-methoxy-1,6-dihydropyrimidin-2,4(1H,3H,6H)dione (XII), 1 -(β-D-ribofuranosyl)-O^5′ -6(S)cyclo-5-diazo-1,6-dihydropyrimidin-2,4(3H,6H)dione (XVII) and 1-(2-deoxy-β-D-ribofuranosyl)-O^5′ -6(S)cyclo-5-diazo-1,6-dihydropyrimidin-2,4(3H,6H)dione (XIX), respectively. Treatment of XII with dimethylamine resulted in a coupling of the 5-diazo group with dimethylamine and a concomitant rearomatization of the heterocyclic ring by expulsion of the 6-methoxy group to furnish 5-(3,3-dimethyl-1-triazeno)uracil (XIV). A similar reaction of XIX and XVII with dimethylamine furnished the corresponding 5-(3,3-dimethyl-1-triazeno)derivatives. The effect which certain resonance hybrids of the diazo moiety may exert in reactions of the above hetero-cycles and the assignment of S configuration at C-6 for the nucleoside derivatives is also discussed.