Sequential Pd(II)−Pd(0) Catalysis for the Rapid Synthesis of Coumarins
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.
[Show abstract] [Hide abstract] ABSTRACT: It is commonly accepted that monoamine oxidase (MAO) may play a critical role in the regulation of the central nervous system activity and contribute to the pathogenesis of human neurodegenerative and depressive disorders. This has encouraged an active research in the development of new drugs, MAO inhibitors, since they may represent an important advance in the treatment of complex diseases such as Alzheimer and Parkinson, which are becoming prevalent pathologies due to the increase of aging population of developed countries societies. Different research groups are intensively working in this area with the aim of finding new MAO selective inhibitors. Differently substituted coumarins have been synthesized and evaluated as MAO-A and MAO-B inhibitors. The purpose of this review is to summarize the findings reported in this area, particularly focuses on the coumarin scaffold.0Comments 16Citations
- "The palladium catalysed chemistry is an alternative methodology for the preparation of 4-substituted coumarin derivatives. 4-Aryl/alkylcoumarins can be obtained from the corresponding phenols by palladium-catalysis reaction with the appropriated propiolates or acrylates . Special mention must be made regarding the arylcoumarin derivatives. "
[Show abstract] [Hide abstract] 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.0Comments 28Citations
- "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. "
- [Show abstract] [Hide abstract] 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.0Comments 104Citations