Chan-Evans-Lam reaction

Scheme 2.19 Putative general mechanism for the Chan-Lam-Evans arylation reaction [12d, 98].

Bruneau et al. [102] showed that it was also possible to conduct this reaction with glucosamines. Pentacetylated aminoglucose and other derivatives could be successfully arylated under Chan-Lam-Evans catalytic conditions (Figure 2.22). The yields were good. 

The reactions in water can be facilitated with an amphiphilic surfactant. Inamoto eial. [105] used these conditions in a catalytic Chan-Lam-Evans arylation of imidazoles with copper(II) acetate and 10 mol% of l,l -dimethyl-2,2 -dipyridyl or its fluorous derivative as ligands at room temperature under air. The best surfactants were BrijSO, Triton-X-100, and the fluorous-type surfactant F-PEG. 

In 2011, Zhuang et al. [133] reported a Chan-Lam-Evans version of the arylation of H-phosphonate diesters using CUjO/phen with arylboronic acids. The reaction was conducted in air... 

Zhu et al. report a domino copper-catalyzed synthesis of benzimidazoles from boronic acids and amidines." This involved a Chan-Lam-Evans Al-arylation, C—H activation, and C—N bond formation (Scheme 7.18). These steps could be carried out in a one-pot reaction to give both primary and secondary benzimidazoles in good yields under mild reaction conditions (Schemes 7.19 and 7.20). 

Evans describes the possibility of a common intermediate for the Ullman and Chan-Lam reactions. D. A. Evans, J. Katz, T. R. West, Tetrahedron Letters 1998, 39, 2937... 

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. 

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. 

In 2000, Guy reported the stoichiometric coupling of alkane thiols and arylboronic acids, which was initially thought to be mediated by Cu(ll) [71]. Liebeskind proposed that the reaction was more likely catalyzed by Cu(l), generated by oxidation of the alkane thiols into dialkyl disulfides. Based on this hypothesis, Liebeskind predicted that disulfides and disulfide equivalents should be effective reagents for thioether formation [34]. This process would constitute a modification of the Chan-Evans-Lam, which involves the coupling of arylboronic acids and amines or alcohols in the presence of tertiary amine bases, generating aryl amines and ethers, respectively. Indeed, the coupling of diphenyl disulfide with phenyl boronic acid would yield diphenyl sulfide. 

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

Reports by the groups of Chan, Evans, and Lam in 1998 revealed an alternative method to conduct copper-mediated couplings that form C(aryl)-0 and C(aryl)-N bonds. In this process, arylboronic acids react with compounds containing N-H or 0-H bonds in the presence of a Cu(II) reagent or catalyst. TTiese reactions were initially conducted with stoichiometric amounts of copper reagents. " Amines, anilines, amides, ureas, carbamates, and sulfonamides underwent N-arylation in moderate to excellent yields by this process (Equation 19.124). The commercial availability of boronic acids and the ability to conduct these arylations in air under mild conditions has caused this method to be adopted quickly for synthetic applications on a small scale. 

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]. 

SCHEME 20.37 Chan-Evans-Lam reaction oxidative cross-coupling. 

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