The reaction of N-propylurea (V) with cyanacetic acid (VI) in hot acetic anhydride gives N-propyl-N'-cyanacetylurea (VII), which is nitrosated with NaNO2 - HCl yielding the isonitroso derivative (VIII). The reduction and simultaneous formylation of (VIII) with Zn in formic acid affords the formylamino compound (IX), which is cyclized by treatment with NaOH to give 6-amino-5-formylamino-1-propylpyrimidine-2,4-dione (X). Finally, this compound is cyclized by treatment with refluxing formic acid. The cyclization of (VII) with NaOH in hot water gives 6-amino-1-propylpyrimidine-2,4-dione (XI), which is nitrosated with NaNO2 - HCl as usual yielding 6-amino-nitroso-1-propylpyrimidine-2,4-dione (XII). The reduction of (XII) with H2 over Pt in DMF affords 5,6-diamino-1-propylpyrimidine-2,4-dione (XIII), which is finally formylated with refluxing formic acid to (X). This compound can also be finally cyclized by treatment with NaOH in refluxing water.

The reaction of 5-amino-4-cyanooxazole (I) with tetramethyl orthocarbonate (II) in refluxing acetic anhydride gives 4-cyano-5-(diethoxymethyleneamino)oxazole (III), which is cyclized with propylamine (A) in refluxing ethanol yielding 5-methoxy-6-propyl-7(6H)-iminooxazolo[5,4-d]pyrimidine (IV), which is finally hydrolyzed and rearranged by treatment with NaOH in water at 100 C or with formamide at 180 C.

The reaction of N-propylurea (V) with cyanacetic acid (VI) in hot acetic anhydride gives N-propyl-N'-cyanacetylurea (VII), which is nitrosated with NaNO2 - HCl yielding the isonitroso derivative (VIII). The reduction and simultaneous formylation of (VIII) with Zn in formic acid affords the formylamino compound (IX), which is cyclized by treatment with NaOH to give 6-amino-5-formylamino-1-propylpyrimidine-2,4-dione (X). Finally, this compound is cyclized by treatment with refluxing formic acid. The cyclization of (VII) with NaOH in hot water gives 6-amino-1-propylpyrimidine-2,4-dione (XI), which is nitrosated with NaNO2 - HCl as usual yielding 6-amino-nitroso-1-propylpyrimidine-2,4-dione (XII). The reduction of (XII) with H2 over Pt in DMF affords 5,6-diamino-1-propylpyrimidine-2,4-dione (XIII), which is finally formylated with refluxing formic acid to (X). This compound can also be finally cyclized by treatment with NaOH in refluxing water.

The reaction of 5-amino-4-cyanooxazole (I) with tetramethyl orthocarbonate (II) in refluxing acetic anhydride gives 4-cyano-5-(diethoxymethyleneamino)oxazole (III), which is cyclized with propylamine (A) in refluxing ethanol yielding 5-methoxy-6-propyl-7(6H)-iminooxazolo[5,4-d]pyrimidine (IV), which is finally hydrolyzed and rearranged by treatment with NaOH in water at 100 C or with formamide at 180 C.

The reaction of N-propylurea (V) with cyanacetic acid (VI) in hot acetic anhydride gives N-propyl-N'-cyanacetylurea (VII), which is nitrosated with NaNO2 - HCl yielding the isonitroso derivative (VIII). The reduction and simultaneous formylation of (VIII) with Zn in formic acid affords the formylamino compound (IX), which is cyclized by treatment with NaOH to give 6-amino-5-formylamino-1-propylpyrimidine-2,4-dione (X). Finally, this compound is cyclized by treatment with refluxing formic acid. The cyclization of (VII) with NaOH in hot water gives 6-amino-1-propylpyrimidine-2,4-dione (XI), which is nitrosated with NaNO2 - HCl as usual yielding 6-amino-nitroso-1-propylpyrimidine-2,4-dione (XII). The reduction of (XII) with H2 over Pt in DMF affords 5,6-diamino-1-propylpyrimidine-2,4-dione (XIII), which is finally formylated with refluxing formic acid to (X). This compound can also be finally cyclized by treatment with NaOH in refluxing water.