Synthesis of 4‐hydrazino‐5 H ‐pyrimido[5,4‐ b ]indole and related compounds

This paper describes the synthesis of two 4‐amino‐5 H ‐pyrimido[5,4‐ b ]indoles 5 , 4‐hydrazino‐5 H ‐pyrimido[5,4‐ b ]indole 6 , two 1,2,4‐triazolo[4,3‐ c ]pyrimido[5,4‐ b ]indoles 8 , and tetrazolo[4,5‐ c ]pyrimido[5,4‐ b ]indole 10 . Starting with ethyl 3‐aminoindole‐2‐carboxylate 1 , 5 H ‐pyrimido[5,4‐ b ]indol‐4‐one 2 was obtained (80%) by condensing with formamide. Reactions of 2 with phosphorus oxychloride and phosphorus pentasulfide gave respectively, 4‐chloro‐5 H ‐pyrimido[5,4‐ b ]indole 3 (70%) and 5 H ‐pyrimido[5,4‐ b ]indole‐4‐thione 4 (80%). Compound 3 reacted with amines (morpholine, piperidine) to give the respective 4‐amino‐5 H ‐pyrimido[5,4‐ b ]‐indoles 5 , and compound 4 reacted with hydrazine to give 4‐hydrazino‐5 H ‐pyrimido[5,4‐ b ]indole 6 (80%). Two hydrazones of 6 (benzylidene, isopropylidene) 7 were also prepared (90%). Compound 6 reacted with formic and acetic acids to give (65–75%) the respective 1,2,4‐triazolo[4,3‐ c ]pyrimido[5,4‐ b ]indoles 8 and with nitrous acid to give tetrazolo[4,5‐ c ]pyrimido[5,4‐ b ]indole 9 (85%). All the new compounds 2 to 9 were characterized by elemental analysis and spectral data (ir, nmr).