C-Nucleosides and related compounds. XII. The synthesis of the carbocyclic analogues of D, L-6-azapseudouridine, 2-thio-6-azapseu douridine, and pyrazofurin A. On the cyclization of semicarbazones of α-keto esters

The preparation of the title compounds is described. The cyclization of the syn- and anti-isomers of semicarbazones, thiosemicarbazones, and carbomethoxymethyl hydrazones to azauracils, thioazauracils, and pyrazoles is described. The photochemical isomerization of the hydrazones has been carried out. Whereas both syn- and anti-isomers of the thiosemicarbazones and carbomethoxymethyl hydrazones cyclize, only the syn-isomer of the semicarbazones can be converted to the corresponding azauracil.