Homocoupling aromatic compounds

Three oxidative reactions of benzene with Pd(OAc)2 via reactive rr-aryl-Pd complexes are known. The insertion of alkenes and elimination afford arylalk-enes. The oxidative functionalization of alkenes with aromatics is treated in Section 2.8. Two other reactions, oxidative homocoupling[324,325] and the acetoxylation[326], are treated in this section. The palladation of aromatic compounds is possible only with Pd(OAc)2. No reaction takes place with PdCl2. 

Oxidation of arylolefins, enolethers, or dienes yields intermolecular homocoupling products in moderate to good yield (see Sect. 13.2.1.4) however, no pronounced diastereoselectivity was observed. This is also due to the fact that the coupling sites do not tolerate substituents that would make up a prostereogenic center. Furthermore, the fairly stable cations of the dimerized radical cation solvolyze stereounselectively. The same holds for the intermolecular coupling of aromatic compounds, in... 

Homocoupling and Oxidative Substitution Reactions of Aromatic Compounds... 

Naphthol is another electron-rich aromatic compound which can also lead to sp -sp CDC-type products. Thus, a new type of Betti base was formed via the CDC reaction of N-phenyl-THIQ with 2-naphthol derivatives under our CuBr/TBHP system with a small amount of homocoupled 2,2-binaphthol (BINOL) (Scheme 1.10). Subsequently, the scope of cross-dehydrogenative Friedel-Crafts type aiylations was significantly improved by the development of highly efficient catalyst systems, and an intramolecular Cu-catalyzed aerobic synthesis of functionalized cinnolines via a Friedel-Crafts-type CDC aiylation was reported by Zhang et al. ... 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

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