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The influence of both electron-withdrawing and electron-donating substituents such as amino, bromo, chloro, ketone, methyl, methoxy, and nitro at C-4 on fluorobenzene derivatives, for palladium-catalyzed direct arylation at α-position to the fluorine atom has been explored. With moderate electron-withdrawing substituents, the reaction proceeds nicely using phosphine-free PdCl2 catalyst, at a very low loading, and potassium pivalate/dimethylacetamide (PivOK/DMA) as catalytic system. In all cases, a regioselective arylation at the α position to the fluorine atom was observed. Moreover, a wide variety of substituents on the aryl bromide coupling partner, such as formyl, nitro, nitrile, chloro, and methyl, and also heteroaryl bromides was tolerated. [ABSTRACT FROM AUTHOR]

In recent years, palladium-catalyzed direct arylation of (hetero)aromatics with aryl halides through a CH bond activation has become a popular method for generating carbon-carbon bonds. A wide variety of heteroaromatics such as furans, thiophenes, thiazoles, or even pyridines can be employed to prepare arylated heterocycles. Conversely, the formation of biphenyl derivatives through CH bond activation has attracted less attention, owing to the lower reactivity of CH bonds of most benzene derivatives. However, over the last few years several new results using modified and improved catalysts and reaction conditions, especially using polyfluorobenzene derivatives, have been reported permitting the synthesis of fluoro-containing biphenyl derivatives at synthetically useful yields. As fluoro-substituents on benzene rings appear to present a very specific effect, which promote such couplings, we summarize here the various methods allowing the synthesis of fluoro-containing biaryls by metal-catalyzed so called 'direct arylation' of (poly)fluorobenzene derivatives. For most of these reactions, aryl halides have been used as the coupling partners, though a several examples employing other coupling partners, such as tosylates or boronic acids, are also known. Moreover, the reaction can be performed with several metal catalysts. This methodology allows the synthesis of complex molecules containing fluorine atoms in only a few steps, and will certainly give the access to a very wide variety of new fluorinated biphenyls useful to both material and biochemists. [ABSTRACT FROM AUTHOR]

The influence of both electron-withdrawing and electron-donating substituents such as nitro, nitrile, chloro, bromo and methoxy at C-3 on fluorobenzenes for their palladium-catalysed direct C-2 arylation has been explored. With electron-withdrawing substituents, the reaction proceeds nicely using 2-4 mol% of an air-stable palladium complex and potassium pivalate/dimethylacetamide (PivOK/DMA) as catalytic system; and in general, a very regioselective arylation at C-2 was observed. Moreover, a variety of substituents on the aryl bromide coupling partner, such as benzoyl, formyl, nitro, nitrile, chloro and methyl, and also heteroaryl bromides were tolerated. [ABSTRACT FROM AUTHOR]