Chan-Lam coupling reactions

Scheme 5.4 Chan-Lam coupling reactions and a simplified catalytic cycle.

Copper has also found wide use however, it has generally only been found to be applicable to heteroatom-carbon coupling reactions when employing boronic acids as coupling partners, now known as the Chan-Lam coupling. ... 

Type of reaction C-N bond formation Reaction conditions Methanol, room temperature Synthetic strategy Chan-Lam coupling forming C-N bond Catalyst Cu(I)Cl/air... 

Finally, C—N bond formation has been also accomplished through aerobic oxidative amination of arylboronic acids (Evans-Chan-Lam coupling) under poly-NHC-copper(II) catalysis. In particular, azoles and aromatic amines were successfully coupled with arylboronic acid using catalyst 73, with catalytic efficiencies comparable to those of other previously reported copper(II)-based catalytic systems for this reaction. 

Compared to the well-established C-N coupling catalyzed by palladium, the copper systems present lower turnover numbers and frequencies. This is particularly the case for the Chan-Lam-type reaction which often still requires stoichiometric amounts of metal. A lot of additives like the oxidant and bases, and sometimes co-oxidants, are also often needed in stoichiometric or higher quantities. 

Arylation of a wide range of NH/OH/SH substrates by oxidative cross-coupling with boronic acids in the presence of catalytic cupric acetate and either triethyl-amine or pyridine at room temperature in air. The reaction works for amides, amines, anilines, azides, hydantoins, hydrazines, imides, imines, nitroso, pyrazi-nones, pyridones, purines, pyrimidines, sulfonamides, sulfinates, sulfoximines, ureas, alcohols, phenols, and thiols. It is also the mildest method for NIO-vinylation. The boronic acids can be replaced with siloxanes or starmanes. The mild condition of this reaction is an advantage over Buchwald-Hartwig s Pd-catalyzed cross-coupling. The Chan-Lam C-X bond cross-coupling reaction is complementary to Suzuki-Miyaura s C-C bond cross-coupling reaction. 

Reactions of Aryl Boronic Acids with Amines and Aicohols (Chan-Evans-Lam Couplings)... 

Oxidative Cross-Coupling (Chan-Evans-Lam Reaction) The coupling of phenols with aryl boronic acids has been accomplished (Scheme 20.37). Initially, Chan and coworkers studied an equivalent amount of CulOAc) for the coupling reaction [58]. Subsequently, Evans and coworkers found the use of MS 4 A led to improvement in the yield of the target product [106]. Later, Lam and coworkers made the process catalytic using oxygen as an oxidant [107]. Their mechanistic aspects have been recently demonstrated [108]. 

The oxidative coupling of a benzoic acid with phenylboronic acid is achievable (Scheme 4.9) [13]. Thus, in the presence of a palladium catalyst together with a silver salt oxidant, decarboxylative coupling takes place selectively to produce 2,4,6-trimethoxybiphenyl. In contrast, under conditions using a copper catalyst in place of Pd, a Chan-Evans-Lam type reaction proceeds to afford phenyl 2,4,6-trimethoxybenzoate. 

Lam P, Clark C, Saubem S, Adams J, Winters M, Chan D, Combs A (1998) New aryl/heteroaryl C-N bond cross-coupling reactions via arylboronic acid/cupric acetate arylation. Tetrahedron Lett 39 2941-2944... 

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. 

Recently, the Chan-Lam reaction was also adapted for the synthesis of aniline derivatives. Indeed, in 2009, Fu et al. described the base- and Ugand-free copper-catalyzed coupling of arylboronic acids with aqueous ammonia (Scheme 30) [234]. This very simple system used 10% of CuzO under air at room temperature and affords the corresponding aniline derivatives in very good yields. The reaction can also be carried out from arylboronic acid esters. A related reaction, performed in water with CUSO4.5H2O as catalyst, was more recently reported by Wu [235]. Fu et al. also reported a quite similar system [236]. 

Since a decade, impressive progressions have been accomplished for the copper-catalyzed formation of C(sp )-N bonds. Both Ullmann and Chan-Lam reactions have permitted the coupling of a wide array of nitrogen nucleophiles with aryl/vinyl halides and boronic acids, respectively. The simplicity of the ligands, when necessary, their commercial availability and the low cost of copper make these reactions very attractive compared to palladium cross coupling, though the latter are considered complementary one to another. 

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