Cross-couplings oxidative

Oxidative cross-coupling reactions of alkylated derivatives of activated CH compounds, such as malonic esters, acetylacetone, cyanoacetates, and certain ketones, with nitroalkanes promoted by silver nitrate or iodine lead to the formation of the nitroalkylated products.67 This is an alternative way of performing SRN1 reactions using a-halo-nitroalkanes. 

With the bisoxazoline hgand (S)-Phbox and CuCl, the asymmetric oxidative couphng of 2-naphthol and hydroxy-2-naphthoates resulted in an asymmetrically substituted 2,2 -binaphthol with ee s of up to 65% [260]. On the basis of the previous results obtained with this catalyst system, the asymmetric oxidative cross-coupling polymerization of 2,3-dihydroxynaphthalene [261] and methyl 6,6 -dihydroxy-2,2 -binaphthalene-7,7 -dicarboxylate [262] as well as the copolymerization of 6,6 -dihydroxy-2,2 -binaphthalene and dihexyl 6,6 -dihydroxy-2,2 -binaphthalene-7,7 -dicarboxylate with Cu diamine catalysts were carried out imder aerobic conditions, using O2 as the oxidant, and a cross-coupling selectivity of 99% was achieved [263]. 

CATALYTIC OXIDATIVE CROSS-COUPLING REACTION OF 2-NAPHTHOL DERIVATIVES... 

Table 8.2 Asymmetric oxidative cross-coupling reaction with CuCl-(5)Phbox...

Oxidative cross-coupling with alkenes is possible with Pd(OAc)2 [109], The reaction proceeds by the palladation of benzene to form phenylpalladium acetate (164), followed by alkene insertion and elimination of /1-hydrogen. Heteroaromatics such as furan and thiophene react more easily than benzene [109]. Stilbene (177) is formed by the reaction of benzene and styrene. The complex skeleton of paraberquamide 179 was obtained in 80% yield by the Pd(II)-promoted coupling of the indole ring with the double bond in 178, followed by reduction of the intermediate with NaBELt [110]. 

Miura, M. Tsuda, T. Satoh, T. Pivsa-Art, S. Nomura, M. Oxidative cross-coupling of N-(2 -phenylphenyljbenzenesulfonamides or benzoic or naphthoic acids with alkenes using a Pd-Cu catalyst system under air. J. Org. Chem. 1998, 63, 5211-5215. 

Dohi T, Ito M, Morimoto K, Wata M, Kita Y (2008) Oxidative cross-coupling of arenes induced by single-electron transfer leading to biaryls by use of organoiodine(III) oxidants. Angew Chem Int Ed 47 1301-1304... 

Setala H, Pajunen A, Rummakko P, Sipila J, Brunow G (1999) A novel type of spiro compound formed by oxidative cross coupling of methyl sinapate with a syringyl lignin model compound. A model system for the b-1 pathway in lignin biosynthesis. J Chem Soc Perkin Trans 1 461 -64... 

As depicted in Equation (97), oxidative cross-coupling of a-aryl-/3,/3-difluoroenol silyl ether with unfunctionalized benzo[ ]furan 82 in the presence of Cu(OTf)2 in wet acetonitrile proceeded smoothly to give benzo[/ ]furan difluoromethyl aryl ketone in 50% yield <2004OL2733>. 

Unsymmetrical 1,4-diketones have been prepared in good yields by (NH4)2[Ce(N03)6] oxidative cross coupling between 1,2-disubstimted and 1-substituted trimethylsilyl eno-lates . The same cerium(IV) compound has been also applied to the preparation of 6-oxo-Q ,/ -unsaturated carbonyl compounds trimethylsilyl dienolates are easily oxidized... 

Coupling reactions. Coupling reactions lead to cinnamate esters and styrenyl ketones. Arylstannanes and arylsilanols can be used as substrates. Oxidative cross-coupling of 2-hydoxybiaryls with alkenes under aeration gives benzochromene derivatives." ... 

SCHEME 101. Oxidative cross-coupling of p-methylphenol and p-methoxy phenol... 

As already shown in Scheme 101, oxidative cross-coupling reactions of two different phenols using DDQ are quite interesting from the viewpoint of natural products synthesis. A mixture of 2,6-di(icri-butyl)phenol (1 equiv.) and 2,6-dimethylphenol (1 equiv.) was also oxidized with Mn(OAc)3 (4 equiv.) to give the desired cross-coupled dimer 674, although the yield (26-10%) was not satisfactory (Scheme 131) . 

As already shown in Scheme 101, an oxidative cross-coupling of two different phenols takes place, but the yield is relatively low. In order for satisfactory cross-coupling to occur it is essential that the phenoxy radicals will be generated to a comparable extent from each of the substrates. Based on biogenetic consideration of benzylisoquinoline alkaloids, extensive studies on oxidative cross-coupling of two different phenols have been undertaken... 

SCHEME 143. Oxidative cross-coupling of 2-naphthol and 2-(p-hydroxyphenyl)ethanol... 

Although not directly relevant to this review, it should be noted that Sanford, Shi and Buchwald have also reported a palladium-catalyzed reaction for the chemo-and regioselective oxidative cross-coupling between ligand coordinated L-Cat-H substrates and simple arenes (Ar-H) [55-57]. 

Pd-Catalyzed Aryl-Aryl Bond Formation via Oxidative Cross-Coupling Reaction. .. 175... 

Scheme 13 Pd-catalyzed oxidative cross-coupling reaction...

Simultaneously, Shi and coworkers used an amide as a directing group in the oxidative cross-coupling reaction. Amide was used as a directing group to control... 

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