Hydrazone derivative (3) was used as a precursor for the synthesis of novel [1,2,4]triazolo [1,5-a]pyridine derivatives via its reaction with some electrophilic reagents. Treatment of hydrazone derivative (3) with arylidenemalononitriles(4) in the presence of piperidine afforded the 1,2,4-triazolo[1,5-a]pyridine derivatives (7a-d). Ternary condensation of hydrazone (3), aliphatic aldehyde and malononitrile (1:1:1 molar ratio) in the presence of a basic catalyst furnished the novel 1,2,4triazolo[1,5-a]pyridine derivatives (8a,b). Similarly, cyclization of hydrazone (3) with ethyl α-cyanocinnamates ( 9) (1:1 molar ratio) yields the corresponding 1,2,4-triazolo[1,5-a]pyridines (10a-c). The hydrazone (3) can be cyclized with appropriate arylazomalononitriles(11) to afford the corresponding 1,2,4-triazolo[1,5-a]pyridines (14a,b). The behavior of fused thiophene derivative (15) towards electron-poor olefins was investigated. It is has been found that, 1,2,4-triazolo[1,5-a]isoquinoline derivative (17) was obtained by treatment of thiophene derivative (15) with dimethyl acetylenedicarboxylate (DMAD). Condensation of compound (15) with N-phenylmalemide furnished pyrrolotriazoloisoquinoline derivative (18). Also, the triazoloisoquinoline derivative (19) was obtained by condensation of compound (15) with chalcone. All the newly synthesized compounds were characterized by analytical and spectral data and evaluated for their antibacterial and antifungal activities in vitro against two Gram-positive bacteria, two Gram negative bacteria as well as two fungi. In general, the newly synthesized compounds showed good antimicrobial activities.
