No abstract

Several new pyrazolo[3,4‐b]pyridines were obtained from the reaction of 5‐amino‐1‐aryl‐3‐methylpyrazoles 1 with β‐dimemylaminopropiophenones 2 in pyridine. The structure elucidation of 4,5‐dihydropyrazolo[3,4‐b]pyridines 3 is based on nmr measurements and X‐ray diffraction. The treatment of compounds 3 with N‐bromosuccinimide led to the formation of pyrazolo[3,4‐b]pyridines 4.

A series of dihydropyrazolo[3,4‐b]pyridin‐6‐ones 3 was prepared by cyclization of 5‐amino‐1‐aryl‐3‐methylpyrazoles 1 and Meldrum's acid benzylidene derivatives 2 in nitrobenzene. The structure of 4,5‐dihydropyrazolo[3,4‐b]pyridin‐6‐ones and reaction orientation were determined by nmr measurements.

Reaction of 5‐amino‐3‐methyl‐1‐phenylpyrazole (1a) and 5‐amino‐3‐(4‐chlorophenyl)‐1H‐pyrazole (1b) with dimedone (2) and p‐susbstituted benzaldehydes 3 in ethanol, afforded in all cases tricyclic linear 4‐aryl‐7,7‐dimethyl‐4,7,8,9‐tetrahydro‐6H‐pyrazolo[3,4‐b]quinolin‐5‐ones (4a‐j) in good yields. The linear structures and hence the regiospecificity of the reaction were established by nmr measurements.

The reaction of 6‐aminopyrimidines 1a, b with dimedone (2) and p‐substituted benzaldehydes 3a‐d in ethanol afforded in all cases new regiospecific synthesis of tricyclic, linear 5‐aryl‐5,6,7,8,9,10‐hexahydropyrimido[4,5‐b]quinolines 4a‐h in good yields. The linear structures and hence the regiospecificity of the reaction were established by nmr measurements.