Sequential Pd(II)−Pd(0) Catalysis for the Rapid Synthesis of Coumarins
Department of Chemistry, 1251 Wescoe Hall Drive, 2010 Malott Hall, University of Kansas, Lawrence, Kansas 66045-7582, USA.The Journal of Organic Chemistry (Impact Factor: 4.72). 09/2005; 70(16):6515-8. DOI: 10.1021/jo050671l
Electrophilic palladium-catalyzed cycloisomerization of brominated aryl propiolates produces brominated coumarins. The brominated coumarins can be diversified by reduction of the Pd(II) catalyst to Pd(0) followed by Suzuki, Sonogashira, 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.
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- "Tunge et al. applied a similar catalyst system to realize the intramolecular hydroarylation of brominated aryl propiolates and sequential Suzuki, Sonogashira, and Heck coupling reaction by addition of other ligands. For example, Pd(OAc) 2 could be used to conduct both the intramolecular hydroarylation and the sequential C-C coupling reaction . As shown in Scheme 47, intramolecular hydroarylation with Pd(OAc) 2 in TFA occurs at room temperature, followed by removal of the TFA, and the flask was then charged with THF, addition of (o-biphenyl)PCy 2 , ptolylB(OH ) 2 , and KF, then heating at 50 o C for 16 h to give coumarin in 88% yield. "
ABSTRACT: Recent advances on the synthesis of six-membered carbo- and heterocyclic compounds including functionalized benzenes, 1,3- cyclohexadienes, pyridines, pyridones, pyranones, coumarins and isocoumarins via the cycloaddition reaction of alkynes are reviewed. Special attention is paid to atom-economic controllable chemo- and regioselective reactions, which are currently extremely attractive methodologies in organic synthesis.
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ABSTRACT: The addition of the C−H bonds of arenes across alkynes is catalyzed by Pd(OAc)2 in CF3CO2H (Fujiwara hydroarylation). Previously it has been suggested that this transformation proceeds by C−H activation of the arene followed by trans-addition of a palladium−arene bond across an alkyne. We have investigated the kinetic isotope effects of intramolecular hydroarylation with deuterated arene substrates and found that catalytic hydroarylation exhibits an inverse KIE. The observed inverse isotope effect is not consistent with known KIEs for C−H activation by electrophilic palladium; thus it suggests that the reaction proceeds by electrophilic aromatic substitution.
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ABSTRACT: A highly divergent, flexible, and conceptually simple sequence allowing the parallel solution-phase assembly of functionalized azinone libraries has been developed in a one-pot consecutive fashion. Structural decoration of in situ-generated heterocyclic aza-Michael adducts AB was accomplished by exploiting the diversity potential of Heck, Suzuki, Sonogashira, and Stille reactions.
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