An efficient Synthesis and Photophysical Properties of 1H-pyrazolo-[3,4-b]pyridine and pyrazolo[3,4-b][1,8]naphthyridines.

A novel synthon 6-amino-3-(4-methoxyphenyl)-1-phenyl-1H-pyrazolo[3,4-b] pyridine-5-carbaldehyde 4 was synthesized by multistep process. Then Friedlander condensation of this synthon with reactive methylenes was performed to achieve interesting tricyclic 6a-b, tetracyclic 6d and pentacyclic 6c N-heterocycles in excellent yield. The absorption and emission spectra of compounds 1-4 and 6 were measured and observed that the absorption and emission depends on the substituent at C-6 and C-7 position of pyridine ring in naphthyridines skeleton 6.