One–pot Selective Synthesis of 2,3‐Dihydro‐4 H ‐Furo[3,2‐ c ]coumarins by Palladium‐Catalyzed Silver‐Assisted Propargylation/Intramolecular 5‐ exo– dig Cyclization

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A new catalytic system using bis(triphenylphosphine)palladium(II) dichloride and Ag 2 CO 3 was developed for the one‐pot selective synthesis of dihydrofuro[3,2‐ c ]coumarin 3 from 4‐hydroxycoumarin ( 1 ) and propargylic carbonate 2 under the mild condition. Our catalytic system afforded distinct regioselectivity compared to reported methodologies using palladium catalysts, 2 and active methylene compounds. In addition, furo[3,2‐ c ]coumarin 4 was derived from 3 with Et 3 N. The proposed reaction mechanism involved 4‐hydroxycoumarin ( 1 ) reacting with the η 1 –(propargyl)palladium complex to generate a terminal alkyne, and subsequent intramolecular 5‐ exo ‐dig cyclization selectively synthesized 3 in one‐pot. The newly developed methodology is beneficial in the construction of a novel compound library related to furocoumarins with distinct regioselective preference.