Ultrasonic-Promoted One-Pot Synthesis of 4H-chromenes, pyrano[2,3- d]pyrimidines, and 4H-pyrano[2,3-c]pyrazoles

Abstract

A facile and versatile procedure has been explored for the synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4Hchromenes, pyrano[2,3-d]pyrimidines and 1,4-dihydropyrano[2,3-c]pyrazole-5-yl cyanides. This protocol employs the one-pot three-component condensation of aromatic aldehydes and malononitrile with 5,5-dimethyl-cyclohexane-1,3- dione, 1,3-dimethyl barbituric acid or 3-methyl-1-phenyl-2-pyrazolin-5-ones respectively in ethanol under the catalytic effect of triethylamine and ultrasonic-irradiation conditions. Simple manipulation, high reaction rates, improved yields, use of inexpensive and non-toxic catalyst, and also use of ethanol as a relatively environmentally benign solvent are the main advantages of this protocol. Keywords: 4H-chromenes, pyrano[2, 3-d]pyrimidines, pyrano[2, 3-c]pyrazole, ultrasonic-irradiation, triethylamine, scaffolds, antibronchitics, microwave, electrochemically, induced