Nitro bromobenzenes

Reaction of potassium phenoxide with p-nitro-bromobenzene in the presence of 18-crown-6 [3] anddibenzo-18-crown-6 111] at 100°C ... 

The compounds formed by nitrating the isomeric nitro-bromobenzenes furnish an illustration of the principle in regard to the orienting effect of substituents on entering groups. The structures of the products formed are shown by the following formulas —... 

Much research has been carried out on the Ugand-free palladium-catalysed Suzuki reaction. Already in 1989, Beletskaya reported a Ugand-free Suzuki reaction in water, between iodobenzoates and phenylboronic acid using Pd(OAc)2 as catalyst [81]. Later, Novak took up the quest to develop a highly active catalyst for the Suzuki reaction and since he noted that this reaction suffers from phosphine inhibition he decided to test three Ugand-free palladium catalyst precursors Pd(OAc)2, [(Ti -CsHsjPd PdCl]2, and Pd2(dba)3.QH6 [82]. All three catalysts performed well in the Suzuki reaction between 4-nitro-iodobenzene and phenylboronic acid. In the reaction with 4-nitro-bromobenzene the first and last catalyst were clearly superior with yields of 96-98% (Scheme 10.7). Novak suggests that... 

The activating effect in the Ullmann coupling reaction of aryl halides provides the electronegative groups such as nitro, alkoxycarbonyl or cyano in the orrAo-position to the halogen atom. These activating substituents present in the meta- or pura-positions do not significantly activate the aryl halide. For example, 2-nitro-bromobenzene reacts with the copper bronze more rapidly and at a lower temperature, while the... 

Moreover, since the cross-coupling reaction of hexaalkyidistannane with aryl halides strongly depends on the reactivity of the latter, a chemoselective cross-coupling of two different aryl halides has become of practical value. Thus Zhang described a simple and versatile method for synthesis of unsymmetrical biaryls from 2-bromopyridines (more reactive) and various phenyl- and 3-pyridyl bromides (less reactive) to afford the appropriate biaryls in moderate to high yields [106]. For example, 5-cyano-2-bromopyridine (167) was cross-coupled with 4-nitro-bromobenzene (168) to give the biaryl 169 in 67% yield [106], respectively, Scheme 23. 

A mixture of hexamethyldistannane (3.00 g, 9.2 mmol, 1.5 eq.), 2-nitro-bromobenzene (94, 1.23 g, 6.1 mmol), and Pd(PPh3)4 (0.20 g, 0.17 mmol, 2.8 mol%) in anhydrous THF (30 ml) was heated to reflux under nitrogen for 10 h. After the mixture was cooled to room temperature, THF was evaporated and dichloromethane (30 ml) was added to the residue. To this mixture, aqueous potassium fluoride (7.0 M, 2 ml) with vigorous stirring was added dropwise. The organic layer was separated, dried and evaporated to dryness The residue was chromatographed over silica gel (100 g) using... 

Methods F and G are ligandless palladium-catalysed and therefore dramatically sensitive to the presence of an oxygen [28]. Beside aryl bromides, the Pd(OAc)2 or Pd(SEt2)Cl2-catalysed SM reactions in A,iV-dimethylformamide were effectively conducted with aryl chlorides [29]. When appropriate precautions were taken, the SM cross-coupling reaction of phenylboronic acid (260) with 4-nitro-bromobenzene (168) or 4-nitro-iodobenzene (225) furnished 4-nitrobiphenyI (224) with a quantitative yield within 0.75 or 2.5 h. Scheme 16. 

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