Synthesis and Reactions of Pyrido[2,1‐a]isoquinolin‐4‐yl Formimidate Derivatives and Antimicrobial Activities of Isolated Products

Treatment of arylidene malononitriles 2A – C with 1‐cyanomethylisoquinoline 1 afforded 4‐amino‐2‐arylpyrido2,1‐a ]isoquinoline‐1,3‐dicarbonitrile derivatives 5A – C , which converted to formimidates 6A – C via reaction with triethylorthoformate. Treatment of the latter compounds with hydrazine hydrate gave the corresponding amino–imino compounds 7A – C , which underwent Dimroth rearrangement to afford 13‐aryl‐1‐hydrazinylpyrimido5′,4′:5,6]pyrido2,1‐a ]isoquinoline‐12‐carbonitrile 8A – C . The latter reacted with aldehyde to give 9a – i . Oxidative cyclization of the latter compounds 9a – i gave 1,2,4]triazolo4″,3″:1′,6′]‐pyrimido5′,4′:5,6]pyrido2,1‐a ]isoquinolines 10a , d , g . Such compounds isomerized to the thermodynamically more stable isomers 1,2,4]triazolo1″,5″:1′,6′]pyrimido5′,4′:5,6]‐pyrido2,1‐a ]isoquinolines 11a , d , g . Antimicrobial activities for some compounds were studied.