Pd/ligand-free synthesis of thienopyranones via Cu-catalyzed coupling-cyclization in PEG 400 under ultrasound

A greener and practical synthesis of 5-substituted thieno[2,3-c]pyran-7-ones has been achieved via Cu-catalyzed coupling-cyclization of 3-iodothiophene-2-carboxylic acid with terminal alkynes in the presence of K2CO3 in PEG 400 under ultrasound irradiation. A range of thienopyranone derivatives were synthesized by using this inexpensive and Pd- and ligand-free methodology.