AbstractThree novel series of pyrazolo[3,4‐b]quinolines were prepared, namely: 1‐(3‐substituted‐4‐phenylthiazolin‐2‐ylidene)hydrazinocarbonylmethyl‐1H‐pyrazolo[3,4‐b]quinolines3a‐d; 1‐(5‐substituted amino‐1,3,4‐thiadiazol‐2‐yl)methyl‐1H‐pyrazolo[3,4‐b]quinolines4b‐d, and 1‐(4‐substituted‐4H‐5‐thioxo‐1,2,4‐triazole‐3‐yl)methyl‐1H‐pyrazolo[3,4‐b]quinolines5a‐d. These compounds were prepared by cyclization of the new key intermediates 1‐(substituted thiocarbamoylhydrazinocarbonyl)methyl‐1H‐pyrazolo[3,4‐b]quinolines2a‐d. The alkylthio, aralkylthio6a‐fas well as theMannichbases8a‐fderived from compounds5a‐dwere also prepared. The structures of the new compounds were elucidated by elemental analyses, IR,1H‐NMR‐, and mass s