Reaction of arylboronic acids having

Palladium-catalyzed reactions of arylboronic acids have been utilized to craft precursors for constructing indole rings. Suzuki found that tris(2-ethoxyethenyl)borane (149) and catechol-derived boranes 150 readily couple with o-iodoanilines to yield 151, which easily cyclize to indoles 152 with acid [158]. Kumar and co-workers used this method to prepare 5-(4-pyridinyl)-7-azaindoles from 6-amino-5-iodo-2-methyl-3,4 -bipyridyl [159], A similar scheme with catechol-vinyl sulfide boranes also leads to indoles [160]. A Suzuki protocol has been employed by Sun and co-workers to synthesize a series of 6-aryloxindoles [161]. 

Palladium-catalyzed reactions of arylboronic acids have been utilized to craft precur-... 

Reaction of Arylboronic Acids Having Highly Steric Hindrance or Electron -withdrawing Functionalities... 

Palladium catalysts have been found which are effective in the Suzuki coupling reaction of arylboronic acids with aryl chlorides carrying electron-withdrawing groups.73 Biaryls may also be synthesized by cross-coupling of arylboronic acids with arenediazonium salts.74,75 There has been a report of the polymer-bound palladium-catalysed Suzuki coupling of aryl triflates with organoboron compounds.76 Arylbor-onates may themselves be synthesized by the palladium-catalysed reactions of... 

After the discovery of a cross-coupling reaction of arylboronic acids with aryl halides or triflates, numerous syntheses of natural and unnatural biaryls have been explored (Equation (204)). 

Arylations. Copper(II) acetate catalyzes the reaction of arylboronic acids with phenols and amines (including imidazole and amides) to provide diaryl ethers (e.g., for synthesis of thyroxine) and arylamines, respectively. The reactions are quite erratic, although some preparatively useful cases have been found. 

Reactions of arylboronic acids with allyl esters have also been found to proceed smoothly in water to give allylic arylation products via a Ti-allylic intermediate with net inversion of configuration (Scheme 22) [90]. It was reported that the secondary allyl esters (alkyl vinyl carbinol esters) undergo j0-hydrogen elimination of the Ti-allylpalladium intermediates forming conjugated dienes under the standard Suzuki-Miyaura coupling conditions due to the relatively lower reactivity of arylboronic acids. 

Olofsson and coworkers have developed several efficient one-pot syntheses of diaryliodonium salts [385-390], A general and universal procedure provides both symmetrical and unsymmetrical diaryliodonium triflates 272 from both electron-deficient and electron-rich arenes 271 and aryl iodides 270 using mCPBA as the oxidant and trifiic acid (Scheme 2.78) [385-387]. The electron-rich diaryliodonium tosylates are prepared similarly using toluenesulfonic acid instead of trifiic acid as the additive [387]. Symmetrical diaryliodonium triflates can be synthesized by a modified one-pot procedure from iodine, arenes, mCPBA and trifiic acid under similar conditions [374,375]. A similar procedure based on a one-pot reaction of arylboronic acids, aryl iodides, mCPBA and BF3 -Et20 has been used for regioselective synthesis of unsymmetrical diaryliodonium tetrafiuoroborates [388,389]. In a further improvement of this approach, a range of... 

Excellent first results have shown the general efficiency in the cross-coupling reactions of arylboronic acids with aryl iodides and bromides, while the reactions with apparently less reactive chlorides failed under this conditions. Further, the SM reaction was significantly developed through a great number of contributions regarding improvements in all above mentioned factors which have strong influence on the reaction efficacy and wide applicability. 

Chloroarenes are an economical and easily available substrate, but they are rarely used for the palladium-catalyzed cross-coupling reaction of arylboronic acids because of their slow oxidative addition to palla-dium(O). Thus, palladium catalysts have been limitedly used for activated chloroarenes, such as chloropyridines (Eq. 44) and electron-deficient chloroarenes ... 

Lam et al. [23] have studied the competition between O- and N-arylation. With 3,5-di-t-butylphenol and 4-t-butylanUine. N-arylation is nine times faster than O-arylation (Scheme 5.22). Since N-arylation is a faster reaction, the side reaction of arylboronic acid converting into the phenol is probably not as pronounced, and thus the use of molecular sieves may not be necessary (vide infra). 

Microwave-assisted Petasis borono-Mannich reactions of arylboronic acids, secondary amines and salicylaldehyde have been carried out in CH2CI2 at 120 °C for 10 min [40], The main problem encountered here was incomplete conversions, resulting in modest adduct yields (23-76%). The reaction of a primary amine (p-ani-sidine) under the same conditions failed to produce the desired adducts, giving instead only the imines (cf. reactions with glyoxylic acid). 

W ang and coworkers have reported the Pd-catalyzed coupling reaction of arylboronic acids with diazo compotmds [84], In 2010, oxidative Pd-catalyzed coupling of Al-tosylhydrazones with arylboronic acids was reported by the same group (Fig. 24) [103]. Under the optimized conditions the reaction of a series of arylboronic acids with substituted acetophenone IV-tosyUiydrazmies proceeds well to afford substimted olefins in acceptable yields. Experimental results indicate that no significant electronic effect and ZIE selectivity have been observed in the reacticMi. 

The development of reaction conditions for the participation of aryl triflates in the Suzuki reaction (725,747,742) expands the synthetic utility of tfiis reaction since triflates are readily obtained from phenols (745). Due to their inherent base sensitivity and thermally lability, mild reaction conditions have been developed for the cross-coupling reaction of arylboronic acids with triflates. High yields are obtained using weak bases, such as powdered K3PO4 or Na2C03, suspended in non-aqueous polar solvents (THF, dioxane) (725,742). Alkali metal halides are added to promote the cross-coupling and/or to prevent the premature catalyst decomposition (725,747). The utilization of more efficient catalysts such as PdCl2(dppf) also permit this reaction to proceed at lower temperatures (725). 

Biphasic systems were found to have a unique effect on the selectivity of the addition of arylboronic acids to alkynes. It was found that the use of [Rh(COD)OH]2 associated with the water-soluble ligand, m-TPPTC, was highly effective for such a reaction in the biphasic water/toluene system (Eq. 4.51).91 The reaction was completely stereo-and regioselective. In addition, the catalyst did not lose any activity... 

So far, no systematic work has been done on the use of recyclable, solid-phase catalysts in cross-coupling reactions. Most of the examples have been obtained for cross-couplings with either arylboronic acids or terminal acetylenes. It should be noted, however, that due care should be exercised when interpreting results on the cross-coupling of arylboronic acids with aryl iodides, as this extremely facile reaction can be catalyzed by practically any palladium-containing material, including trivial Pd black,481 e.g., as a sediment on the reaction vessel. Therefore, this reaction cannot serve as a reliable test for comparison between different catalytic systems. 

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