I2-promoted tandem cyclization to synthesize polysubstituted pyrano[3,2-c]chromene-2,5-diones

Abstract An efficient and convenient method for the synthesis of various substituted pyrano[3,2-c]chromene-2,5-diones was developed via the I2-promoted tandem cyclization of commercially available aryl methyl ketones and 4-hydroxycoumarins. Preliminary mechanism studies indicated that the reaction involved a consecutive iodination/Kornblum oxidation/annulation process. HI produced in the I2-DMSO system acted as an important promoter, accelerating the annulation protocol.