Palladium compounds from boronic acids

Thus, for our present purposes a similar approach was followed using Suzuki cross-coupling reactions as the key steps in the synthesis of our target compounds. Symmetrically substituted compounds were synthesized in a twofold Suzuki crosscoupling reaction from commercially available p-substituted phenylboronic acids or esters and 4,4 -dibromobiphenyl or 4,4 -biphenyl-bis-boronic acid ester and a p-substituted arylhalide, respectively, using tetrakis (triphenylphosphino) palladium as catalyst together with cesium fluoride as base in dry tetrahydrofurane as shown in Scheme 8.1. The desired products were obtained in respectable yields after heating at reflux for 50 h. 

In general it is not advisable to have the palladium-catalysed coupling reaction as last or penultimate step in view of the need to reduce palladium levels in the final product to below 10 ppm. Based on this reasoning, Taiwanese chemists patented an alternative route towards Lapatinib in which the furan ring is coupled to the quinazoline moiety before attachment of the substimted aniline (Scheme 23) [69]. Thus, coupling between the furfural-boronic acid 99 and aryl halide 103 catalysed by a catalyst prepared in situ from palladium acetate and one equivalent of tri-t-butylphosphine (2 mol%) gave the biaryl compound 104 in 98% HPLC yield. 

Additionally, symmetric ketones have also been produced by the carbonylative homo-coupling of organometallic reagents [94-99]. Under the assistant of palladium catalysts and under the pressure of carbon monoxide, ketones were produced from alkenyl- and arylborates and boronic acids, diaryliodonium salts, organolead compounds and arylmercuric salts. [Rh(CO)2Cl]2 was also applied as a catalyst for the carbonylative homo-coupling of vinyl- and arylmercurials. 

Boronic acids and boronate esters serve a myriad of purposes, and the discovery of the Suzuki-Miyaura reaction facilitated the widespread interest and application of organoboron compounds. This palladium-catalyzed C-C bond forming reaction initiated renewed interest in the preparation of diversely functionalized boronic acids that would lead to valuable products. From this synthetic standpoint, Suzuki coupling reactions have been employed in the production of natural products and the preparation of materials of interest. " The search for interesting starting materials for the Suzuki reaction produced a series of methods to prepare boronic acids so these species could be exploited in further applications. These compounds... 

Arylboronic acids and esters serve as aryl group donors for palladium-catalyzed arylation procedures." The boronic acids are readily prepared from an aryllithium compound and trimethyl borate, followed by hydrolysis. The boronic acids react... 

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