Oxidation biaryl coupling

Thieno benzazepine 109 was synthesized in moderate yield by oxidative biaryl-coupling using the hypervalent iodine reagent phenyliodine(lll)bis (trifluoroacetate) (FIFA) and BF3 OEt2 as the activating agent in methylene chloride (Equation (16) (2002X8581)). 

Kita and Tohma found that exposure of p-substituted phenol ethers to [bis(tri-fluoroacetoxy)iodo]benzene 12 in the presence of some nucleophiles in polar, less nucleophilic solvents results in direct nucleophilic aromatic substitution [Eq. (84)] [156]. Involvement of a single-electron transfer (SET) from phenol ethers to A3-iodane 12 generating arene cation radicals was suggested by the detailed UV-vis and ESR studies. SET was involved in the oxidative biaryl coupling of phenol ethers by 12 in the presence of BF3-Et20 [157]. 

In the intermolecular mode, this reaction has been utilized for the preparation of products 28 from various nucleophiles, including C-nucleophiles (e. g. (3-dicarbonyl compounds). A similar reaction in the intramolecular mode provides a powerful synthetic tool for the preparation of various polycyclic compounds via oxidative biaryl coupling [21,27 - 30]. Several examples of these C-C bond forming reactions are shown in Schemes 13-15. Specifically, various dibenzoheterocyclic compounds 30 have been prepared by the oxidation of phenol ether derivatives 29 with [bis(trifluoroacetoxy)iodo]benzene in the presence of BF3-etherate in dichloromethane (Scheme 13) [27-29]. 

Concise total synthesis of a promising antiviral (anti-HIV) agent, michel-lamine A (58), was accomplished by Bringmann and Tasler via oxidative biaryl coupling reaction of korupensamine A (166) using PIFA (or Pb(OAc)4)-BF3 Et20 [128] (Scheme 35). 

Another example of intramolecular oxidative biaryl coupling in the synthesis of allocolchicine-type structures was provided by the total synthesis of the allocolchicinoidjerusalemine 9, Fig. (13) [31]. 

Cyclopropane 106 was obtained by two routes in the first route, the conjugated ester 104 (R=Me, >95%. E-isomer) underwent oxidative biaryl coupling in the presence of TTFA to give biaryl cycloheptene 105 in good... 

Li X, Hewgley JB, Mulrooney CA, Yang J, Kozlowski MC (2003) Enantioselective oxidative biaryl coupling reactions catalyzed by 1, 5-diazadecalin metal complexes efficient formation of chiral functionalized BINOL derivatives. J Org Chem 68 5500-5511... 

Additional examples of intramolecular oxidative coupling of phenolic ethers include the oxidative biaryl coupling of various N-substituted 1-benzyltetrahydroisoquinolines 313 to the corresponding aporphines 314 [374], the oxidative cyclization of 3,4-dimethoxyphenyl 3,4-dimethoxyphenylacetate (315) leading to the seven-membered lactone 316 [375] and the conversion of phenol ether derivatives 317 into the products of... 

Based on their mechanistic investigation on the Cu -mediated oxidative coupling of 2-naphthol derivatives, Smrcina, Kocovsky, and co-workers were able to develop the first catalytic asymmetric oxidative biaryl coupling reaction (Scheme 3.3). AgCl was used as the stoichiometric oxidant to regenerate the Cu species. In order to avoid the formation of detrimental HCl by-product, the corresponding sodium 2-naphthol salts were employed as the coupling partners. The desired product 3 was obtained in 41% yield (8 turnovers) with 32% ee. 

Scheme 3.3 The first catalytic asymmetric oxidative biaryl coupling reaction reported by Smrcina and Kocovsky.

Table 3.1 Asymmetric aerobic oxidative biaryl coupling reactions reported by Nakajima.

Scheme 3.5 An overall catalytic cycle proposed for the asymmetric aerobic oxidative biaryl coupling catalyzed by chiral Cu-diamine complex.

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