- A new gold-catalyzed domino cyclization and oxidative coupling reaction
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Gold-catalyzed domino cyclization and oxidative coupling reaction for synthesis of dicoumarins was studied. Gold was thought to be an unreactive metal before its catalyzed reaction was discovered. HAuCl4 was suspended in dry 1,2-dichloroethane (DCE), whereas protic solvent gave only monomer and UV absorption and fluorescence properties of dicoumarins were similar to those of monomers. The crude product was purified by flash column chromatography on silica and gold catalyst performed two different functions. Dicoumarins, scaffolds of natural products has interesting biological properties whereas, potential photostable UV-absorbent materials were accessed in two steps from commercially available starting materials. The reaction generally proceeded in moderate-to-good yields, tolerating a variety of substituents on the aromatic moiety.
- Wegner, Hermann A.,Ahles, Sebastian,Neuburger, Markus
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supporting information; experimental part
p. 11310 - 11313
(2009/10/17)
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- Preparation of new tert-butyl substituted coumarins, thiocoumarins and dithiocoumarins
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6-tert-Butyl-4-methyl- and 6,8-di-tert-butyl-4-methylcoumarin were prepared from tert-butylphenols and diketene via the corresponding aryl acetoacetates. 6-tert-Butyl-4-methyl-thiocoumarin (6) was obtained from 6-tert-butylthiophenol. Thionation with Lawesson's or Davy's reagent led to the related thion- and dithiocoumarins. The structures were proved by NMR spectroscopy and an X-ray structure analysis of 6.
- Voss, Jrgen,Edler, Ronald,Adiwidjaja, Gunadi
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p. 1893 - 1905
(2008/02/10)
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- New Method for Preparation of Coumarins and Quinolinones via Pd-Catalyzed Intramolecular Hydroarylation of C-C Triple Bonds
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A new and general method has been developed for preparation of coumarins and quinolinones by intramolecular hydroarylation of alkynes. Various aryl alkynoates and alkynanilides undergo fast intramolecular reaction at room temperature in the presence of a
- Jia, Chengguo,Piao, Dongguo,Kitamura, Tsugio,Fujiwara, Yuzo
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p. 7516 - 7522
(2007/10/03)
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- Novel Pd(II)- and Pt(II)-catalyzed regio- and stereoselective trans-hydroarylation of alkynes by simple arenes
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Efficient trans-hydroarylation of alkynes by simple arenes has been realized regio- and stereoselectively at room temperature in the presence of Pd(II) or Pt(II) catalysts and a mixed solvent containing trifluoroacetic acid (TFA). Various arenes undergo trans-hydroarylation selectively across terminal and internal C - C triple bonds - including those conjugated to CHO, COMe, CO2H, and CO2Et groups, affording kinetically controlled cis-arylalkenes predominantly in most cases, especially, in good yields for electron-rich arenes and activated alkynes. The formation of arene/alkyne 1/2 or 2/1 adducts as side products is dependent on the arenes' and alkynes' substituents, which can be suppressed in some cases by changing the catalyst, catalyst concentration, and reaction time. The Pt(II) system, PtCl2/2AgOAc/TFA, shows lower catalytic activity than Pd(OAc)2/TFA, but higher selectivity, giving higher yields of adducts at the same conversion. On the basis of several isotope experiments and control reactions, a possible mechanism involving electrophilic metalation of aromatic C - H bonds by in-situ-generated cationic Pd(II) and Pt(II) species leading to intermolecular trans-arylpalladation to alkyes has been discussed.
- Jia, Chengguo,Lu, Wenjun,Oyamada, Juzo,Kitamura, Tsugio,Matsuda, Kenji,Irie, Masahiro,Fujiwara, Yuzo
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p. 7252 - 7263
(2007/10/03)
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