Synthesis of polysubstituted pyridines under combined microwave and ultrasound irradiation: K2CO3-promoted tandem addition/cyclization/hydrogen shift process

A convenient and efficient K2CO3-promoted tandem reaction of chalcone, malononitrile, and methanol for the synthesis of highly functionalized pyridines has been developed. This multi-component reaction employing the weak nucleophilic agent methanol proceeded smoothly under combined microwave and ultrasound irradiation (CMUI). The reaction mechanism was proposed to consist of a Michael addition, a methoxylation of CN bond, a cyclization to a 1,4-dihydropyridine and an intermolecular hydrogen shift between 1,4-dihydropyridine and initial chalcone.