Al(OTf)3-Catalyzed Preparation of 4-Hydroxy-3-propargylic Coumarins and Subsequent Regioselective Cyclization towards Furo- or Pyrano[3,2-c]coumarins
摘要:
An efficient and economical approach to functionalized furo[3,2-c]coumarin and pyrano[3,2-c]coumarin derivatives has been developed from 4-hydroxy-3-(prop-2-ynyl)coumarin derivatives through organocatalysis or metallo-organocatalysis. Selective 5-exo-dig' or 6-endo-dig' cyclization of the 4-hydroxy-3-(prop-2-ynyl)coumarin substrates could be achieved under organocatalytic {1,8-diazabicyclo[5.4.0]undec-7-ene} or metallo-organocatalytic (N-methylmorpholine/CuBr) conditions, respectively, to yield potentially bioactive heterocycles in excellent yields.