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(3 H )dione (XI), 5‐diazo‐6‐hydroxy‐1,6‐dihydropyrimidin‐2,4(1 H ,3 H ,6 H )dione (XIII), 5‐diazo‐6‐methoxy‐1,6‐dihydropyrimidin‐2,4(1 H ,3 H ,6 H )dione (XII), 1 ‐(β‐D‐ribofuranosyl)‐ O 5′ ‐6( S )cyclo‐5‐diazo‐1,6‐dihydropyrimidin‐2,4(3 H ,6 H )dione (XVII) and 1‐(2‐deoxy‐β‐D‐ribofuranosyl)‐ O 5′ ‐6( S )cyclo‐5‐diazo‐1,6‐dihydropyrimidin‐2,4(3 H ,6 H )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.