Microwave-assisted, facile route to 1H-pyrazolo[3,4-b]quinolines

Abstract

Aromatic aldehydes have been reported to react with 5-anilinopyrazoles in the presence of ZnCl2 to give the corresponding benzylidenopyrazoles. In this paper evidence is given that the corresponding products are, in fact, 1H-pyrazolo[3,4-b]quinolines. This observation opens a novel route to these compounds. They show a blue emission in the solid state and, therefore, they are useful blue luminophores for electroluminescent devices. The synthetic procedure reported in the literature was significantly modified and improved by application of microwave heating. In our modified synthesis the reaction time was reduced from the usual 5 to 8 h to 5 to 7 min and the reaction products were formed without contamination.