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Phase-transfer Gomberg-Bachmann reactions

With many heterocycles as substrates, radical substitutions can be successfully carried out under the conditions of phase-transfer Gomberg-Bachmann reactions [145]. Again, as above, mainly aryl and heteroaryl halides have recently been used as precursors for heterobiaryl compounds. A study including the arylation of a large number of heterocycles in the presence of tributyltin hydride and catalytic benze-neselenol led to the results that mostly biaryl products are obtained from nitrogen-containing heterocycles, whereas furan and thiophene gave partially dearomatized compounds [155]. [Pg.55]

The Gomberg-Bachmann reaction is usually conducted in a two-phase system, an aqueous alkaline solution, that also contains the arenediazonium salt, and an organic layer containing the other aromatic reactant. Yields can be improved by use of a phase transfer catalyst. Otherwise yields often are below 40%, due to various side reactions taking place. The Pschorr reaction generally gives better yields. [Pg.141]

Mixed hiaryls. The synthesis of biaryls by the Gomberg-Bachmann reaction of aryidiazonium salts and arencs can be conducted to advantage under phase-transfer catalysis using potassium acetate to form a diazo anhydride. KOAc can be replaced by NaOH, KOH, or K2CO3, but with lower yields. [Pg.70]

Complexation with crown ethers increases the notoriously low solubilities of diazonium salts in most solvents (with the obvious exception of water). Therefore, it is possible to carry out phase-transfer reactions with complexed diazonium ions (review Gokel et al., 1985). Useful examples can be found in a paper from Gokel s group (Beadle et al., 1984a) on the Gomberg-Bachmann and Pschorr reactions (see Sec. 10.10). [Pg.301]

Gomberg-Bachmann biphenyl synthesis. Reaction of stable arenediazonium tet-rafluoroborates or hexafluorophosphates in an aromatic solvent with potassium acetate (2 equiv.) and a phase-transfer catalyst results in biar Is in high yield. Crown ethers, Aliquat 336, and tetrabutylammonium hydrogen sulfate arc all effective catalysts. The reaction is useful for synthesis of unsymmetrical biaryls. The ortho-isomer predominates in reactions with a monosubstituted benzene. The most selective method is to couple a substituted arenediazonium salt with a symmetrical arene. [Pg.380]


See other pages where Phase-transfer Gomberg-Bachmann reactions is mentioned: [Pg.51]    [Pg.168]    [Pg.287]    [Pg.287]    [Pg.928]    [Pg.715]    [Pg.1248]    [Pg.121]    [Pg.254]    [Pg.924]    [Pg.505]    [Pg.38]    [Pg.38]    [Pg.244]   
See also in sourсe #XX -- [ Pg.51 ]




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