Sadao Nishigaki

A New, Convenient Synthesis of 2-Alkyl- and 2-Vinylpyrazolo [3,4-d]pyrimidine Derivatives

Treatment of 1,3-dimethyl-6-hydrazinouracil with the appropriate dimethylformamide dialkylacetal afforded the, corresponding 2-alkyl-5,7-dimethylpyrazolo[3,4-d]pyrimidine-4,6-(5H,7H)diones. The reaction of 1,3-dimethyl-6-(α-methylbenzylidenehydrazino)uracils with dimethylformamide dimethylacetal or triethyl orthoformate gave the corresponding 5,7-dimethyl-2-vinylpyrazolo[3,4-d]pyrimidine-4,6(5H,7H)diones, respectively. Similarly, treatment of 1,3-dimethyl-6-(α-methylbenzylidenehydrazino)uraeils with triethyl orthopropionate yielded the corresponding 5,7-dimethyl-3-ethyl-2-vinylpyrazolo[3,4-d]pyrimidine-4,6(5H,7H)diones.

1,3-Dipolar cycloaddition of a thiazolo [5,4-d]pyrimidine 1-oxide to dimethyl acetylenedicarboxylate. New ring transformation to a pyrrolo-[3,2-d]pyrimidine via a pyrimido [4,5-b][1,4]thiazine

1,3-Dipolar cycloaddition of a thiazolo[5,4-d]-pyrimidine 1-oxide to dimethyl acetylenedicarboxylate resulted in the ring transformation of the thiazole moiety to give a pyrrolo [3,2-d] pyrimidine via a pyrimido [4,5-b]thiazine.

A new purine synthesis

Reaction of 6-amino-5-nitrosouracil derivatives with various substituted hydrazones of aldehydes led to the formation of the corresponding xanthine derivatives.

A new synthesis of alloxazines

The treatment of 6-anilino-4-hydroxy-5-p-nitro-phenylazo-2-phenylpyrimidines with 10% concentrated sulphuric acid in glacial acetic acid led to the formation of the corresponding 2-phenyl-2-deoxyalloxazines.

A new pteridine synthesis

The reaction of 6-amino-5-(1,2-diethoxycarbonylhydrazino)pyrimidines with enamines represents a convenient method for the preparation of pteridines.