Selective Pd-catalyzed oxidative coupling of anilides with olefins through C-H bond activation at room temperature

Using a high-throughput experimentation approach we found a selective and mild Pd-catalyzed oxidative coupling reaction between anilide derivatives and acrylates that occurs through ortho C-H bond activation. The reaction is carried out in an acidic environment and occurs even at room temperature with use of a cheap oxidant (benzoquinone) in yields up to 91%. The benzoquinone possibly also functions as a ligand, stabilizing the catalyst. From the electronic dependence of the reaction and the observed kinetic isotope effect (kH/kD = 3) the key step of the catalytic cycle is believed to be electrophilic attack by a [PdOAc]+ complex on the pi-system of the arene.     

Direct ortho-acetoxylation of anilides via palladium-catalyzed sp(2) C-H bond oxidative activation

Various anilides have been directly ortho-acetoxylated through a Pd(OAc)2-catalyzed C-H bond activation process. The amide group in anilides was found to functionalize as an elegant directing group to convert aromatic sp(2) C-H bonds into C-O bonds in high regioselectivity with acetic acid as the acetate source and K(2)S(2)O(8) as the oxidant.     

Rhodium- and iridium-catalyzed oxidative coupling of benzoic acids with alkynes via regioselective C-H bond cleavage

The oxidative coupling of benzoic acids with internal alkynes effectively proceeds in the presence of [Cp*RhCl2]2 and Cu(OAc)2 x H2O as catalyst and oxidant, respectively, to produce the corresponding isocoumarin derivatives. The copper salt can be reduced to a catalytic quantity under air. Interestingly, by using [Cp*IrCl2]2 in place of [Cp*RhCl2]2, the substrates undergo 1:2 coupling accompanied by decarboxylation to afford naphthalene derivatives exclusively. In this case, Ag2CO3 acts as an effective oxidant.     

Mechanistic studies of Pd-catalyzed regioselective aryl C-H bond functionalization with strained alkenes: origin of regioselectivity

Mechanistic studies of a palladium-catalyzed regioselective aryl C-H functionalization of 2-pyrrole phenyl iodide with norbornene are presented. Kinetic and spectroscopic analyses together with crystallographic data provide evidence for intermediates in a proposed stepwise mechanism. On the basis of the mechanistic studies, the origin of the regioselectivity is due to a ligand exchange between I(-) and HO(-) on the norbornyl palladium complex. These mechanistic studies also implicate that either alkoxide or water is responsible for the formation of the palladacycle, but a reversible ring-opening-ring-closing process of the palladacycle with HX can retard the rate of reaction of a key intermediate. The significant aspects of the proposed mechanism are discussed in detail.     

Mild aerobic oxidative palladium (II) catalyzed C-H bond functionalization: regioselective and switchable C-H alkenylation and annulation of pyrroles

A palladium catalyzed C-H bond functionalization system that operates under ambient and aerobic conditions can be used to alkenylate pyrroles with control of regioselectivty. A steric and electronic control strategy can be used to influence positional control in the C-H bond functionalization process that results in either the C2 or C3 alkenylated products. Air, molecular oxygen, or tBuOOBz can be used as reoxidant in this mild process, and the reaction works on a range of substrates. Finally a catalytic aerobic annulation strategy is described that can be controlled to produce cyclization at either the C2 or C3 positions, thus forming diverse pyrrole products.     

Pd-catalyzed regioselective C-H chlorination of disubstituted 1,2,3-triazoles

This paper mainly studied Pd-catalyzed regioselective chlorination of disubstituted 1,2,3-triazoles directed by the 1,2,3-triazole ring. A series of regioselective chlorinated products were synthesized in 47–86% yields using Pd(OAc)₂ as a catalyst and CuCl₂ as a chlorinated reagent. This method provides a new mean for the synthesis of 1,2,3-triazole halides which combines the formation of C-X bond with C-H activation.     

Catalytic C-H bond functionalization with palladiumII: aerobic oxidative annulations of indoles

A palladium-catalyzed aerobic oxidative annulation of indoles is described. We have demonstrated that a variety of factors influence these cyclizations, and in particular the electronic nature of the pyridine ligand is crucial. It is also remarkable that these oxidative cyclizations can proceed in good yield despite background oxidative decomposition pathways, testament to the facile nature with which molecular oxygen can serve as the direct oxidant for Pd(0). We have also shown that the mechanism most likely involves initial indole palladation (formal C-H bond activation) followed by migratory insertion and beta-hydrogen elimination.     

Nickel-catalyzed chelation-assisted transformations involving ortho C-H bond activation: regioselective oxidative cycloaddition of aromatic amides to alkynes

Although the pioneering example of ortho metalation involving cleavage of C-H bonds was achieved using a nickel complex (Kleiman, J. P.; Dubeck, M. J. Am. Chem. Soc. 1963, 85, 1544), no examples of catalysis using nickel complexes have been reported. In this work, the Ni-catalyzed transformation of ortho C-H bonds utilizing chelation assistance, such as oxidative cycloaddition of aromatic amides with alkynes, has been achieved.     

Palladium-catalyzed direct and regioselective C-H bond functionalization/oxidative acetoxylation of indoles

The first general examples of palladium-catalyzed direct and selective oxidative C3-acetoxylation of indoles are presented. The mild reaction conditions (70 °C and with weak base, KOAc) in this indole C-H-acetoxylation are notable.     

Ruthenium-catalyzed oxidative vinylation of heteroarene carboxylic acids with alkenes via regioselective C-H bond cleavage

The ruthenium-catalyzed oxidative vinylation of thiophene-2-carboxylic acids with alkenes efficiently proceeds through directed C-H bond cleavage to give the corresponding 3-vinylated products. Similarly, benzothiophene-, benzofuran-, pyrrole-, and indolecarboxylic acids also undergo regioselective vinylation.     

基于C-H键活化的铜催化二苄胺氧化酰胺化反应

基于铜催化的C-H键活化构建了一类高效的二苄胺氧化酰基化生成N-苄基苯甲酰胺的反应. 该反应使用CuBr作为催化剂, 二乙酸碘苯作为氧化剂, 在温和条件下生成两种酰胺, 总产率最高可达92.0%. CuBr催化剂价廉易得, 催化活性高. 同时这也是首次使用二乙酸碘苯作为氧化剂, 通过二苄胺的直接氧化酰基化反应合成N-苄基苯甲酰胺.     

Pd-catalyzed double C-H bond activation of diaryl ketones for the synthesis of fluorenones

An efficient synthesis of fluorenones from diaryl ketones by Pd-catalyzed oxidative cyclization is described. A possible mechanism involving a carbonyl group assisted ortho-C-H activation and cyclometalation followed by a second C-H activation to form a six-membered palladacycle and reductive elimination is proposed.     

Rhodium-catalyzed regioselective C-H functionalization via decarbonylation of acid chlorides and C-H bond activation under phosphine-free conditions

Efficient rhodium(I)-catalyzed regioselective functionalization of aromatic C-H bonds has been realized with acid chlorides as the coupling partners via decarbonylation and C-H activation under phosphine-free conditions.     

Iron-catalyzed direct arylation through directed C-H bond activation

An iron-catalyzed C-C bond formation reaction of a nitrogen-containing aromatic compound with an arylzinc reagent takes place at 0 degrees C in a good to quantitative yield. The reaction involves a C-H bond activation directed by a neighboring nitrogen atom. The important additives in this reaction are 1,10-phenanthroline, tetramethylethylenediamine, and 1,2-dichloro-2-methylpropane, in the absence of which a very low product yield was observed.     

One-pot amidation of olefins through Pd-catalyzed coupling of alkylboranes and carbamoyl chlorides

A one-pot synthesis of C1-elongated amides starting from olefins and carbamoyl chlorides has been developed. Alkylboranes, generated by hydroboration of terminal olefins with 9-BBN-H, underwent smooth coupling with carbamoyl chlorides in the presence of palladium catalyst and Cs2CO3.     

Pd-catalyzed arylation/oxidation of benzylic C-H bond

A palladium-catalyzed benzylic C-H arylation/oxidation reaction leading to diaryl ketones has been accomplished. The indispensable role of the bidentate system is disclosed for this sequential process. This chemistry offers a direct new access to a range of diarylketones.     

Intermolecular coupling of alkenes to heterocycles via C-H bond activation

The intermolecular coupling of unactivated alkenes to a range of heterocycles using a Rh(I) catalyst was investigated. A variety of functional groups were incorporated into the alkene, including esters, nitriles, acetals, and phthalimide. Furthermore, the heterocycle tolerated substitution with both electron-rich and electron-deficient groups. The intermolecular coupling became possible after it was discovered that weak acids dramatically increase the rate of both the inter- and intramolecular reactions. An extensive optimization of additives was performed, and HCl.PCy(3) (Cy = cyclohexyl) and HCl.P-t-Bu(2)Et were in general found to be the best additives for the reaction.     

C-C bond formation via double C-H functionalization: aerobic oxidative coupling as a method for synthesizing heterocoupled biaryls

The aerobic oxidative coupling of arenes such as benzofuran and N-substituted indoles with benzene and derivatives thereof is described. The reaction is shown to take place in both inter- and intramolecular scenarios.