A Pd-Catalyzed Heteroannulation Approach to 2,3-Disubstituted Furo[3,2-c]coumarins
摘要:
The Pd-catalyzed cyclofunctionalization of 3-alkynyl-4-methoxycoumarins with aryl halides resulted In the selective formation of 3-arylfuro[3,2-c]coumarins in lieu of the expected regioisomeric 3-arylfuro[2,3-b]chromones. A mechanism involving the linear to angular rearrangement of a Pd-containing furan intermediate was proposed.
The reaction of 3-alkynyl-4-methoxycoumarins with molecular iodine in chlorinated solvents allows access to 3-iodofurochromones in good to excellent yields as the result of a iodocyclization–demethylation process. Competitive diiodination of the coumarin acetylene moiety could be eliminated by simply performing the reactions in refluxing 1,2-dichloroethane, owing to the thermal instability of the resulting (E)-1,2-diiodoethenylcoumarins.
The Pd-catalyzed cyclofunctionalization of 3-alkynyl-4-methoxycoumarins with aryl halides resulted In the selective formation of 3-arylfuro[3,2-c]coumarins in lieu of the expected regioisomeric 3-arylfuro[2,3-b]chromones. A mechanism involving the linear to angular rearrangement of a Pd-containing furan intermediate was proposed.