Phenylboronic acids Suzuki-Miyaura cross-coupling

The reaction of interest was first reported by Miyaura and co-workers in 1997 [1]. It was found that the addition of phenylboronic acid, a reagent pioneered for Pd-catalysed Suzuki-Miyaura cross-coupling, to simple a,p -unsaturated ketones was catalysed by Rh(I) complexes. 

Synthesis and Cytostatic Activity of Substituted 6-Phenylpurine Bases and Nucleosides Application of the Suzuki—Miyaura Cross-Coupling Reactions of 6-Chloropurine Derivatives with Phenylboronic Acids... 

Figure 3.63). The palladium(II) complex was used in the Suzuki-Miyaura cross-coupling reaction between phenylboronic acid and benzyl bromide, 2-bromo and 4-bromo benzalde-hyde, respectively [180-182],...

A convenient and effective palladium-catalysed Suzuki-Miyaura cross coupling reaction of deactivated aryl chlorides with phenylboronic acid utilised the 1,3-diazepinium salts 107 as in situ precursors of the palladium ligands. These salts were prepared from the diamines 106 and cyclocondensation with triethyl orthoformate <05SL2394>. 

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. 

During the course of an investigation into the Suzuki-Miyaura cross-coupling of l-bromo-2,4,6-tri-tert-butylbenzene with phenylboronic acid, a, a -dimethyl-)8-phenyl dihydrostyrene by-product was isolated in excellent yield, while the desired biaryl product was not observed. This unexpected transformation likely proceeded via a pathway involving a tandem C-H activation/ Suzuki-Miyaura cross-coupling sequence (eq 40). ... 

The Suzuki-Miyaura cross-coupling reaction of the synthetically versatile aryl O-carbamate is applied in the construction of heterotriaryls 39 and 41 (Scheme 14.11). Heterobiaryl O-carbamates 38 and 40, both previously prepared by a DoM-Suzuki-Miyaura cross-coupling sequence, are involved in a Ni-catalyzed O-carbamate cross-coupling with phenylboronic acid to afford their corresponding heterotriaryls 39 and 41, respectively, in poor and excellent yields [64]. 

Miyaura N, Yanagi T, Suzuki A (1981) The palladium-catalyzed cross-coupling reaction of phenylboronic acid with haloarenes in the presence of bases. Synth Commun 11 513... 

Mechanistic knowledge of the Suzuki-Miyaura reaction is far from complete [22d, 23], Although a base is obligatory and phenylboronic acids are known to form borates at high pH, evidence is not available for an RB(OH)3 intermediate. Especially intriguing, compared with other cross-coupling processes, is the unknown step. 

For the Suzuki coupling reactions, see (a) Miyaura, N., Yanagi, T, and Suzuki, A., The palladium-catalyzed cross-coupling reaction of phenylboronic acid with haloarenes in the presence of bases, Synth. Comm., //, 513 (1981) (b) Suzuki, A., Organoborates in new synthetic reactions, Acc. Chem. Res., 15, 178-184 (1982) (c) Huber, J., and Scherf, U., A soluble poly(para-phenylene) composed of cyclophane units poly(2,5-(oxydecanoxy)-l,4-phenylene] Macromol. Rapid Commun., 15, 897 (1994). 

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