Amide formation arylboronic acids

Reactions between a representative range of alkyl- and aryl-amines and of aliphatic and aromatic acids showed that the direct formation of amides from primary amines and carboxylic acids without catalyst occurs under relatively low-temperature conditions (Scheme 1). The best result obtained was a 60% yield of N-bcnzyl-4-phenylbutan-amide from benzylamine and 4-phenylbutanoic acid. For all these reactions, an anhydride intermediate was proposed. Boric and boronic acid-based catalysts improved the reaction, especially for the less reactive aromatic acids, and initial results indicated that bifunctional catalysts showed even greater potential. Again, anhydride intermediates were proposed, in these cases mixed anhydrides of carboxylic acids and arylboronic acids, e.g. (I).1... 

This reaction allows aryl carbon-heteroatom bond formation via an oxidative coupling of arylboronic acids, stannanes or siloxanes with N-H or O-H containing compounds in air. Substrates include phenols, amines, anilines, amides, imides, ureas, carbamates, and sulfonamides. The reaction is induced by a stoichiometric amount of copper(II) or a catalytic amount of copper catalyst which is reoxidized by atmospheric oxygen. 

Interestingly, it is evident that the reactivity of boric acid is better at high temperatures, and it declines at lower reaction temperatures. Subsequently, a wide variety of boron-based reagents, such as catechol and arylboronic acid-based catalysts, have been developed for direct amide formation. The enhancement of the Lewis acidity of boron has been proven to enhance catalytic activity e.g. chlorocatechol derivative 9 or 10), as in eqn (13.2). ... 

Hayashi and Miyaura pioneered the enantioselective rhodium-catalyzed conjugate addition of arylboronic acids to a variety of Michael acceptors a,P-unsaturated ketones, esters, lactones, amides, and lactams [215]. Generally, water is used as a cosolvent and plays a key role in the catalytic cycle, illustrated in Scheme 5.111 (cycle A) for the conjugate addition of phenylboronic acid to cyclohexenone that, when catalyzed by the Rh(I)-(S)-BINAP complex, leads to 3-phenylcyclohexanone in 97% ee and 93% chemical yield [205a]. The key intermediates of the catalytic cycle, the hydroxorhodium complex 433, the phenylrhodium complex 434, and -bound rhodium enolate 435 were characterized by NMR spectroscopy. The reaction of the hydrorhodium complex 433 with phenylboronic acid leads to a transmetallation to give the phenylrhodium complex 434. Then, the insertion of the carbon-carbon double bond of cyclohexenone into the phenylrhodium bond leads to the formation of the... 

This chapter covers more specifically the copper-catalyzed C(aryl)-N bond formation via the coupling of aryl halides with nitrogen nucleophiles such as N-heterocycles, amines, anilines, amides, ammonia, azides, hydroxylamines, nitrite salts or phosphonic amides. The C(aryl)-N bond formation as a result of the coupling between these nucleophiles and arylboronic acids (the Chan-Lam reaction) will be also presented. It is worth noting that this chapter mainly focuses on the most significant results and important breakthroughs in this field. 

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