Bromobenzene, cross-coupling reactions

The atom economy of the cross-coupling reaction and the Heck reaction for making styrene from bromobenzene and vinyl bromide (cross), and bromobenzene and ethene (Heck) respectively are in favour of the Heck reaction, as that produces only one equivalent of salt. 

The organometallic-substituted 85 (M = a derivative of B, Zn, Sn) and halogeno-substituted siloles 85 (M = C1, Br, I) are suitable starting compounds for cross-coupling reactions. Pd-catalyzed coupling of 91 (R = Me, Ph) with 4-amino- and 4-heteroaryl-bromobenzenes affords the siloles 92 in high yield <20040M6205>. 

Fig. 16 Suzuki cross-coupling reaction between bromobenzene and phenylboronic acid...

Palladium complexes of TPPTS and TPPMS have been employed extensively as catalysts for carbonylation, hydroxycarbonylation, and C—C cross-coupling reactions (cf. Section 6.6). Hydroxycarbonylation of bromobenzene in biphasic medium using Pd(TPPTS)3 as catalyst yields benzoic acid, which remains in the aqueous phase, thus avoiding the direct recycling of the catalyst [59]. The formation of Pd(TPPTS)3 from PdCl2 and TPPTS in aqueous solution has been studied in detail by 170, 1H 31P, and 35C1 NMR spectroscopy. The complex [ PdCI(TPPTS)3 Cl obtained initially is reduced by excess TPPTS, TPPTSO being formed. A more attractive synthesis of Pd(TPPTS)3 involves the facile reduction of [PdCl-(TPPTS)3]+C1- with CO (Scheme 1) [60],... 

The Suzuki-Miyaura cross-coupling reaction is a standard method for carbon-carbon bond formation between an aryl halide or triflate and a boronic acid derivative, catalyzed by a palladium-metal complex. As with the Mizoroki-Heck reaction, this cross-coupling reaction has been developed in ionic liquids in order to recycle and reuse the catalyst. In 2000, the first cross-coupling of a halide derivative with phenylboronic acid in [bmim] [BF4] was described. As expected, the reaction proceeded much faster with bromobenzene and iodobenzene, whereas almost no biphenyl 91 was obtained using the chloride derivative (Scheme 36). The ionic liquid allowed the reactivity to be increased, with a turnover number between 72 and 78. Furthermore, the catalyst could be reused repeatedly without loss of activity, even when the reaction was performed under air. Cross-coupling with chlorobenzene was later achieved - although with only a moderate yield (42%) - using ultrasound activation. 

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. 

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. 

The collection of different nanoparticles having different designed sizes is crucial to the study of the mechanisms in nanoparticle catalysis. These click dendrimer-stabiUzed nanoparticles are efficient catalysts for selective olefin hydrogenation under ambient conditions, and the turnover Ifequencies, turnover numbers and yields depend on the nanoparticle size. The smallest nanoparticles (from Gi) are the most active ones, in agreement with a classic hydrogenation mechanism entirely proceeding at the nanoparticle surface [66]. On the other hand, the turnover numbers, turnover frequencies and yields are independent on the type of nanoparticle stabilization and sizes of the nanoparticles for the Suzuki cross coupling reaction between chlorobenzene or bromobenzene and PhB(OH)2. Moreover, the... 

Subsequently, a copper-catalyzed cross-coupling [with substoichiometric amounts of copper(l) iodide and N,N -dimethylethylenediamine (DMEDA)] between aryl halides and sulfoximines was developed [52]. In this case, both aryl bromides and aryl iodides reacted well. For the conversion of the former substrates an in-situ copper-catalyzed aryl Finkelstein reaction [53] had to be performed first, as shown in Scheme 2.1.1.22 for the preparation of 64 starting from bromobenzene (62). 

The Suzuki-Miyaura tactic carried out on solid support (Scheme 28) [52] provides routes to small libraries of condensed heterocycles. Thus, Merrifield resin with the LeznofF-linked bromobenzene derivative 78 undergoes cross-coupling under normal solution-phase conditions with boron pinacolate 79 or boronic acid 80, prepared by DoM, to afford phenan-thridines 81 or, via 82 and some manipulation, dibenzopyranones 83 in good yields and with high purities. The Stille solid-support reaction has also been successfully executed [53]. 

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