Copper-Catalyzed Synthesis of Furo[3,2-c]coumarins and Dihydrofuro[3,2-c]coumarins through a Propargylation/Alkyne Oxacyclization/Isomerization Cascade under Microwave Irradiation

摘要

A novel copper-catalyzed microwave-promoted propargylation/alkyne oxacyclization/isomerization cascade for the synthesis of 2-methylfuro[3,2-c]coumarins has been developed. This reaction provides furo[3,2-c]coumarins in moderate to good yields (82%) from readily available 4-hydroxycoumarins and terminal propargyl acetates as starting materials. Interestingly, by changing the solvent from dimethyl sulfoxide to 1,2-dichloroethane, the isomeric series of 2-methylene-2,3-dihydrofuro[3,2-c]coumarins were obtained in good to acceptable yields (85%).