Phenylboronic Suzuki coupling with aryl bromides

Reetz and coworkers reported the use of Pd and Pd/Ni clusters stabilized by tetrabutylammonium salts for the Suzuki coupling of aryl bromides and chlorides with phenylboronic acid [38], The bimetallic Pd/Ni clusters were found generally to be more reactive, reacting also with activated aryl chlorides. 

Lately, Bradley and coworkers reported the use of Pd particles (7.4 nm) captured in cross-linked polystyrene-PEG resin as efficient, stable against leaching and recyclable catalysts in the Suzuki coupling of aryl bromides with phenylboronic acids [51]. 

Pyrazole-tethered Schiff base ligands 62 promoted Suzuki cross-couplings of aryl bromides and chlorides with phenylboronic acid efficiently under mild conditions <05TL15>. Chromium-trioxide complex with 3,5-dimethylpyrazole 63 oxidation of cyclohexenecarbonitrile provided 3-oxocyclohex-1 -ene-1 -carbonitrile <05S3179>. 

Table 2.11 Suzuki-Miyaura Coupling of Aryl Bromides With Phenylboronic Acid —cont d...

Acyclic aminocarbenes have not been used widely as ligands for transition metal catalysts. The amino(aryl)carbene complexes 26 and 27 are rare examples that showed moderate activity in the Suzuki coupling of aryl iodides and bromides with phenylboronic acid (Figure 5.7). ... 

Suzuki coupling reactions with aryl halides. Two as-prepared BaCei cPd c03. ( materials (x = 0.05 and 0.10) were successfully utihzed in several Suzuki coupling reactions. Both aryl iodides and aryl bromides react smoothly with 4-phenylboronic acid, eq 1, to yield the corresponding biatyls in high yields (> 95%). For both 4-bromoanisole and 4-iodoanisole, the biatyl yields reached nearly 100% in 3 min with BaCeo 95Pdoo503 5 as the catalyst, corresponding to an effective TON of ca. 2,000 and an effective TOF of nearly 50,000 h. Resnlts are smmnarized in Table 27.1. 

Most recently, Monteiro et al. have reported that cyclopalladated compounds derived from the ortho-metalation of benzylic tert-butyl thioethers are excellent catalyst precursors for the Suzuki cross-coupling reaction of aryl bromides and chlorides with phenylboronic acid under mild reaction conditions. A broad range of substrates and functional groups are tolerated in this protocol, and high catalytic activity is attained (Eq. (58)) [93]. 

A traceless solid-phase synthetic strategy has been developed. For example, a solid-phase Suzuki coupling of the Reissert intermediate 30 to 31 has been reported. The process consists of three steps (a) Solid-phase Reissert formation by the reaction of polymer-supported benzoic acid chloride resin with an isoquinoline, followed by reaction with TMSCN to afford the aryl bromide of Reissert 30, (b) Suzuki coupling of the solid-phase Reissert 30 with phenylboronic acid to provide the coupling product, and (c) subsequent treatment of the coupling product with aqueous KOH to produce 31 (86 % overall yield based on the starting bromide) (Eq. (62)) [99]. 

Early examples of the total synthesis of naturally occurring indole alkaloids employing the Suzuki reaction include ellipticine (10) as repotted by Miller et al. [34], The aryl bromide, 6-amino-7-bromo-5,8-dimethylisoquinoline (45) was derived from 2,5-dimethylanilinc in nine steps. The Suzuki coupling of 45 with phenylboronic acid was carried out using catalytic tetrakis(triphenylphosphine)palladium in benzene and with Na,CO, serving as the base to furnish... 

Palladium species immobilized on various supports have also been applied as catalysts for Suzuki cross-coupling reactions of aryl bromides and chlorides with phenylboronic acids. Polymers, dendrimers, micro- and meso-porous materials, carbon and metal oxides have been used as carriers for Pd particles or complexes for these reactions. Polymers as supports were applied by Lee and Valiyaveettil et al. (using a particular capillary microreactor) [173] and by Bedford et al. (very efficient activation of aryl chlorides by polymer bound palladacycles) [174]. Buch-meiser et al. reported on the use of bispyrimidine-based Pd catalysts which were anchored onto a polymer support for Suzuki couplings of several aryl bromides [171]. Investigations of Corma et al. [130] and Plenio and coworkers [175] focused on the separation and reusability of Pd catalysts supported on soluble polymers. Astruc and Heuze et al. efficiently converted aryl chlorides using diphosphino Pd(II)-complexes on dendrimers [176]. 

The performance of complex 10 bearing a quinolinylidene as a remote car-bene ligand (Figure 5.5) was compared to that of simple imidazol-2-ylidene and phosphine-containing palladium catalysts in the Heck coupling of activated and non-activated aryl bromides with butyl acrylate. " The remote carbene complex showed much higher activity in these reactions as well as in the Suzuki coupling of a deactivated aryl bromide with phenylboronic acid. Since the complexes tested were structurally very different, purely electronic comparisons... 

The Suzuki reaction was described in the presence of various [Pd(7 -allyl)Cl]2 (l)/ligand systems as well. The efficiency of the tetraphosphine ligand Tedicyp was demonstrated for various Suzuki couplings, and more recently for the reaction of alkenyl-boronic acids with arylbromides. 7i The preparation of various stryrene derivatives (eq 81) has been performed in the presence of vinylboronic acid and substituted alkenyl boronic acids. The catalyst system was tolerant of electronic variation in the aryl-bromide component. Tum-over numbers of 3100-8600 could be achieved for activated substrates such as 4-bromoacetophenone. The coupling of alkyl tosylates was described either in the presence of Pd(OAc)2 or dimer (1) as precursor. 7 a fiber-supported catalyst prepared from 1 was found to be efficient for Suzuki coupling between activated aryl bromides and phenylboronic acid. 

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