Synthesis of Pyrazolo[3,4-b]pyridines and Pyrido[2,3-d]pyrimidinones by Hetero-Diels-Alder Reaction of Pyrazolyl- and Pyrimidinilimines under Microwave Irradiation in Dry Media

Microwave irradiation in dry media induces pyrazolyl- la and pyrimidinil-2-azadiene lb to undergo hetero-Diels-Alder reaction with 3-dimethylaminopropiophenone hydrochlorides 2 within 2-3 minutes to give good yields of 5-aroylpyrazolo[3,4-b]pyridines 3a-c and 6-aroylpyrido[2,3-d]pyrimidinones 4a-c. The structure of compounds 3 and 4 and regiochemistry of reaction were determined on the basis of nmr measurements.