- Palladium-catalyzed C-H bond direct alkynylation of 5-membered heteroarenes: A well-defined synthetic route to azole derivatives containing two different alkynyl groups
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A widely applicable oxidative coupling of 5-membered heteroarenes and terminal alkynes that uses a combination of palladium and silver salts was developed. Under suitable conditions, imidazole and benzimidazole, which are sluggish under similar previously reported oxidative coupling conditions, as well as imidazo[1,5-a]pyridines, oxazole, benzoxazole, thiazole, and benzothiazole could be alkynylated. In addition, the bromine atom on the substrates was intact under the reaction conditions, and conventional Sonogashira coupling did not occur at all. With these reactivities in hand, a well-defined synthetic route to imidazo[1,5-a]pyridines and thiazole containing two different alkynyl groups was achieved in a simple manner. In addition, linear correlations were observed between the fluorescence wavelength and the Hammett substituent constants of aryl groups, not only on the C1- but also on the C3-alkynyl group of the obtained 1,3-bis(arylethynyl)imidazo [1,5-a]pyridines.
- Shibahara, Fumitoshi,Dohke, Yoshimasa,Murai, Toshiaki
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supporting information; experimental part
p. 5381 - 5388
(2012/08/27)
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- A straightforward copper-free palladium methodology for the selective alkynylation of a wide variety of S-, O-, and N-based mono- and diheterocyclic bromides and chlorides
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High-yield alkynylations are successfully achieved by a simple and widely accessible catalytic system for an unprecedented variety of heterocyclic bromides and chlorides in position -2, -3 or -5: pyridine, quinoline, thiophene, furan, thiazole, benzothiazole, pyrimidine, pyridazine, pyrazine, dioxepin halides are efficiently functionalized in short time reactions. This copper-free methodology employs 1 mol % palladium only, with inexpensive PPh3 and amine base. The ionic liquid solvent allows a straigtforward separation of products and recycling opportunity. Unsuitable substrates and secondary reactions are also reported in order to point out further progress in cross-coupling using ionic liquids.
- Saleh, Samer,Picquet, Michel,Meunier, Philippe,Hierso, Jean-Cyrille
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experimental part
p. 7146 - 7150
(2009/12/06)
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- Reductive coupling of halogenothiophenes and halogenothiazoles catalysed by PdII in a basic alcohol medium
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A catalytic reductive coupling method has been developed whereby 2- and 3-bromo- and 2-iodothiophenes, 2-bromothiazole and 2-bromofuran are converted into their corresponding bithiophene, bithiazole and bifuran derivatives. The use of a basic alcohol medium favours the reductive coupling pathway over the hydrodehalogenation pathway, which is generally more facile when other reducing agents are used. The catalytic mechanisms are discussed. The syntheses and characterization of the proposed intermediate complexes, trans-[PdBr(C4H3S-C)(PPh3)2] 1, trans-[PdI(C4H3S-C)(PPh3)2] 2 and trans-(N,P)-[{PdBr(μ-C3H2NS-C2,N)(PPh 3)}2]·1/2CHCl3 3 support the proposed mechanism and the catalytic results. Single-crystal X-ray crystallographic structure determinations of 2 and 3 were carried out.
- Xie, Yang,Tan, Geok Kheng,Yan, Yaw Kai,Vittal, Jagadese J.,Ng, Siu Choon,Hor, T. S. Andy
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p. 773 - 779
(2007/10/03)
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- THIONYL CHLORIDE - A GOOD LIGAND COUPLING REAGENT
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Thionyl chloride was found to react with phenylethynyllithium and heteroaryllithium affording 1,4-diphenylbutadiyne and biheteroaryl, and the corresponding sulfoxides and sulfides, respectively.Apparently, ligand coupling proceeded within the intermediary sulfurane.The occurrence of ligand coupling was estimated from the pKa value of the carbon acid as a nucleophile.Furthermore, it was found that the presence of p-orbital, i.e., ?-bond, is preferable at the ipso carbon atom of the nucleophile for a good ligand coupling reaction, while for alkyllithiums and alkylmagnesium chloride do not give bialkyl as the main coupling product, but others, which are different from the organic lithiums or magnesium chloride used. Key words: Thionyl chloride, hypervalent, ligand coupling, sulfurane
- Oae, Shigeru,Inubushi, Yoichi,Yoshihara, Masakuni
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p. 101 - 110
(2007/10/02)
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- UNSYMMETRICAL HETEROBIARYL SYNTHESIS. A HIGHLY EFFICIENT PALLADIUM-CATALYZED CROSS-COUPLING REACTION OF HETEROARYL TRIALKYLSTANNANES WITH ARYL HALIDES
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A general synthesis of heterobiaryls in good yields via Pd-catalyzed cross-coupling of trialkylheteroarylstannanes 1-5 with aryl halides is described.
- Bailey, Thomas R.
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p. 4407 - 4410
(2007/10/02)
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