Sequential Pd(Ⅱ)-Pd(0) Catalysis for the Rapid Synthesis of Coumarins

摘要

Electrophilic palladium-catalyzed cycloisomerization of bro-minated aryl propiolates produces brominated coumarins. The brominated coumarins can be diversified by reduction of the Pd(Ⅱ) catalyst to Pd(0) followed by Suzuki, Sonoga-shira, Heck, or Hartwig—Buchwald coupling. Thus, a single loading of precatalyst can be used to conduct sequential reactions, allowing the synthesis of functionalized coumarins. Extension of this methodology toward the synthesis of coumarin libraries is discussed.