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

This paper describes the synthesis of two 4-amino-5H-pyrimido5,4-b]indoles 5 , 4-hydrazino-5H-pyrimido5,4-b]indole 6 , two 1,2,4-triazolo4,3-c]pyrimido5,4-b]indoles 8 , and tetrazolo4,5-c]pyrimido5,4-b]indole 10 . Starting with ethyl 3-aminoindole-2-carboxylate 1 , 5H-pyrimido5,4-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-5H-pyrimido5,4-b]indole 3 (70%) and 5H-pyrimido5,4-b]indole-4-thione 4 (80%). Compound 3 reacted with amines (morpholine, piperidine) to give the respective 4-amino-5H-pyrimido5,4-b]-indoles 5 , and compound 4 reacted with hydrazine to give 4-hydrazino-5H-pyrimido5,4-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-triazolo4,3-c]pyrimido5,4-b]indoles 8 and with nitrous acid to give tetrazolo4,5-c]pyrimido5,4-b]indole 9 (85%). All the new compounds 2 to 9 were characterized by elemental analysis and spectral data (ir, nmr).