Arylboronic acids cross-coupling reactions

Microwave and fluorous technologies have been combined in the solution phase parallel synthesis of 3-aminoimidazo[l,2-a]pyridines and -pyrazines [63]. The three-component condensation of a perfluorooctane-sulfonyl (Rfs = CgFiy) substituted benzaldehyde by microwave irradiation in a single-mode instrument at 150 °C for 10 min in CH2CI2 - MeOH in the presence of Sc(OTf)3 gave the imidazo-annulated heterocycles that could be purified by fluorous solid phase extraction (Scheme 9). Subsequent Pd-catalyzed cross-coupling reactions of the fluorous sulfonates with arylboronic acids or thiols gave biaryls or aryl sulfides, respectively, albeit it in relatively low yields. 

Apart from imidazol-2-ylidene carbenes, other electron-rich carbenes such as (L27)—generated by deprotonation of a 4,5-dihydroimidazole—have been tested for cross-coupling reactions, but gave much poorer results. The only reported exception is in the cross-coupling of arenediazonium salts with arylboronic acids, in which (L27) (used as hydrochloride) proved to be efficient.369... 

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. 

Fukuyama, Y., Y. Kiriyama, and M. Kodama. 1993. Concise synthesis of belamcan-daquinones A and by palladium (0) catalyzed cross-coupling reaction of bromo-quinone with arylboronic acids. Tetrahedron Lett. 34 7637-7638. 

The carbonylative cross-coupling reactions of haloazines are usually run under an ambient to moderate carbon monoxide pressure. Arylboronic acids or tetraarylborates are usually the reagent of choice due to their robustness and availability. The coupling of 2-iodopyridine and phenylboronic acid under ambient CO pressure, for example, led to the formation of 2-benzoylpyridine in good yield (7.66.),87... 

Watanabe, T. Miyaura, N. Suzuki, A. Synthesis of sterically hindered biaryls via the Pd-cat-alyzed cross-coupling reaction of arylboronic acids or their esters with haloarenes. Synlett 1992, 207-210. 

Saito, S. Oh-tani, S. Miyaura, N. Synthesis of biaryls via a Ni(0)-catalyzed cross-coupling reaction of chloroarenes with arylboronic acids./. Org. Chem. 1997, 62, 8024-8030. 

Aryltetrazoles (131) and 5-vinyltetrazoles are prepared by the palladium-catalyzed cross coupling reaction of bromotetrazole (130) with arylboronic acids in >90% yields [95TL1679]. The tetrazolium salt (133) was prepared by the NCBT closure of the formazan (132) [94H73]. 

N. Miyaura, Synthesis of Biaryls via the Cross-Coupling Reaction of Arylboronic Acids, in Advances in Metal-Organic Chemistry (L. S. Liebeskind, Ed.), JAI Press, Greenwich, 1998, 6, 187-243. 

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