Aryl halides, coupling reactions

Biphenyl bond formation has been achieved in the diiodobiaryl derivative 41 by an intramolecular aryl halide coupling reaction promoted by tetrakis(tri-phenylphosphine) nickel. This short and efficient route gave the dibenzazonine 42 in good yield (42) (Scheme 9). In a similar way, tetrasubstituted derivative 43 was successfully coupled with the more easily prepared tris(triphenylphos-phine)nickel, giving 44 in 62% yield. Subsequent debenzylation led to the most efficient synthesis of dibenzazonine 35a reported to date (43). 

In comparison to the nickel-catalysed aryl halide coupling reactions, the palladium-catalysed analogues are not sensitive to the steric hindrances and to the presence of nitro group. The nickel(O) complexes are more reactive than the appropriate palladiums, and thus more effective in the reactions with the least reactive aryl chlorides. However, the palladium complexes are more convenient and selective, even in the cross-coupling reaction of two electronically different aryl halides. 

In a related reaction, aryl halides couple with vinyl tin reagents to form styrene derivatives in the presence of a nickel catalyst, for example, ... 

Coupling of organostannanes with halides in a carbon monoxide atmosphere leads to ketones by incorporation of a carbonylation step.249 The catalytic cycle is similar to that involved in the coupling of alkyl or aryl halides. These reactions involve Reactions involving a migration of one of the organic substituents to the carbonyl carbon, followed by... 

Although not directly analogous to the coupling of thiols with aryl halides, the reaction of thiourea with an aryl halide in the presence of palladium catalyst, nevertheless, can be used to generate a thiophenol from an aryl halide after hydrolysis (Equation (39)).129 This process occurred in greater than 90% yield with a variety of simple aryl halides ... 

The decomposition of triarylselenonium halides was reported to produce aryl halide. jhis reaction is likely to proceed through a ligand coupling mechanism. 

Cobalt(II) catalyses the coupling of Grignard reagents with chloropyridines"° and of aryl cuprates with aryl halides. This reaction shows unusual substrate reactivity patterns and the mechanism is thought to involve a radical intermediate at the oxidative addition step. 

Ullmann reaction Semmelhack (4, 33) has shown that bis( 1,5-cyclo-octadiene)nickel(O) and tetrakis(triphenylphospine)nickel(0) are useful reagents for coupling of aryl halides (Ullmann reaction). However, these zerovalent nickel complexes are not easy to prepare and are extremely sensitive to moisture. Kende reasoned that the coordinatively unsaturated Ni(TPP)3 is actually the species involved and indeed found that aryl halides couple to biaryls in the presence of 1 eq. of this complex. Aryl halides with two orr/io-substituents do not couple. Otherwise, yields of biaryls are in the range of 60-80%. 

In the presence of Bu-P4 base and copper(I) bromide, aryl halides couple with phenols to give biaryl ethers at about 100 °C, while the use of DBU as a base for this coupling reaction is not effective [50] (Scheme 5.31). 

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