基于铁催化的C-H键活化构建C-C键的研究进展

过渡金属催化的C-H键活化及在此基础上的C-C键形成的反应因其高原子经济性和高效的合成效率而备受人们的关注.铁元素具有含量丰富、廉价、易得、环境友好等优点,在催化反应中得到了越来越广泛的应用.近几年来,人们关于Fe催化的C-H键活化构建C-C键反应的研究也取得了一定的进展.本文对铁催化的C-H键活化构建C-C键的最新研究进展作了综述,并且按照铁催化剂的不同价态进行了分类归纳,也对催化机理进行了阐述与总结.     

Copper-catalyzed oxidative trifluoromethylation of benzylic sp C-H bond adjacent to nitrogen in amines

Copper-catalyzed trifluoromethylation via oxidative sp³ C-H activation at the α-position of nitrogen in tetrahydroisoquinoline derivatives using DDQ and Ruppert-Prakash reagent has been successfully achieved. The reaction of various amines gave the corresponding trifluoromethylated products in 15-90% yields under mild conditions.     

Radical-mediated intramolecular C-C bond formation and the deoxygenation of alcohols under solvent-free conditions with tributyl methyl ammonium hypophosphite

A green, solvent-free protocol was developed for the radical-mediated intramolecular cyclization of haloacetals and the deoxygenation of S-methyl dithiocarbonates and cyclic thionocarbonate. This process uses tributyl methyl ammonium hypophosphite as a H-donor in the presence of triethylborane or t-butyl peroxide. This methodology provides eco-friendly reaction conditions.     

Silver-catalyzed direct couplings of 2-substituted furans with cyclic 1,3-dicarbonyls

Direct alkenylation of 2-substituted furans with cyclic 1,3-dicarbonyls by means of silver catalysis have been explored. Silver salts resulted more efficient than a variety of Lewis acids and p-TsOH.     

Metal-free synthesis of 2-aminothiadiazoles via TBHP-Mediated oxidative C-S bond formation

An efficient one-pot synthesis of 2-amino-1,3,4-thiadiazoles from easily available aldehydes and thiosemicarbazide using TBHP as an oxidant has been described. Notably, these reactions were carried out at room temperature using ethanol as solvent. This is the first example for one-pot synthesis of 2-amino-1,3,4-thiadiazole derivatives from aldehydes. This new synthetic methodology provides a simple procedure utilizing a safer oxidizing system that affords the target products in mild reaction condition with satisfactory yields and wide substrate scope.     

A DDQ-promoted metal-free cross-coupling of 1,3-diarylpropynes with hydroxyl via Sp C-H bond activation to form C-O bond

A metal-free coupling reaction between 1,3-diarylpropynes and alcohols/phenols/acids via propargylic sp³ C-H bonds activation and C-O bond formation reaction promoted by DDQ was realized. The reaction afforded series of propargyl ethers, propargyl esters and propargyl ketals.     

A new diastereoselective multicomponent, one-pot strategy for the synthesis of 3-substituted isoindolinones via efficient C-C bond formation

A new three-component reaction among o-phthalaldehyde, N-alkyl/aryl substituted urea, and an aromatic aldehyde has been developed at ambient condition, and a class of isoindolinones with novel C-3 substitution were conveniently synthesized. The general diastereomeric excess as high as over 99% of the products indicated the excellent stereoselectivity posed in this multicomponent reaction.     

Rhodium-catalyzed alkylation of terephthaldialdimine with terminal alkenes via C-H bond activation

Terephthaldialdimine 1a reacted with alkenes to give 2,6-dialkylated products selectively in moderate to high isolated yields. In the case of terephthaldialdimine 1b having a substituent at site 2 in the phenyl ring, the alkylation takes place selectively at site 6 in the phenyl ring. In this alkylation, a meta-substituent affected the reactivity significantly because of the steric hindrance.     

Rhodium-catalyzed alkylation of aromatic azines with alkenes via C-H bond activation

The aromatic azines reacted with terminal alkenes under a rhodium catalyst [RhCl(coe)₂]₂ and Cy₃P to give the alkylated products with good to high isolated yields. The azines bearing H and o-CH₃, p-CH₃ and p-CH₃O groups have high reactivities, but m-CH₃O, p-Cl, p-F exhibit low reactivities.     

Oxazoline Chemistry. Part 11: Syntheses of natural and synthetic isoflavones, stilbenes and related species via C-C bond formation promoted by a Pd-oxazoline complex

The complex trans-[PdCl₂(2-ethyl-2-oxazoline-κ¹N)₂] (1) is shown to be an active and oxidatively robust catalyst for C-C bond forming reactions (Heck, Sonogashira, Ullmann, Miyaura-Suzuki, etc.). These reactions can be carried out in air without rigorous solvent/substrate purification and in the absence of additional free ligand. The general methodology described above has been applied to the high yield and regio-selective formation, via Miyaura-Suzuki coupling, of natural and synthetic isoflavones (i.e., isoflavone, 2′-methylisoflavone [7b], 3′-methylisoflavone [7c] and 3′,4′-benzoisoflavone: [7d]). Compounds 7c and 7d are previously unknown. In addition, the synthesis of (E)-tris-O-methylresveratrol and (E)-3,5-dimethoxystilbene is also described; the former is a recognized anti-cancer agent while the latter is a biologically active extract from the bark of the conifer species Pinus armandii. Both of these latter products are produced as a result of a Heck coupling reaction promoted by 1.     

Intermolecular oxidative C-N bond formation under metal-free conditions: control of chemoselectivity between aryl sp2 and benzylic sp3 C-H bond imidation

A new synthetic approach toward intermolecular oxidative C-N bond formation of arenes has been developed under transition-metal-free conditions. Complete control of chemoselectivity between aryl sp(2) and benzylic sp(3) C-H bond imidation was achieved by the choice of nitrogen sources, representatively being phthalimide and dibenzenesulfonimide, respectively.     

Copper-catalyzed oxidative CH bond functionalization of N-allylbenzamide for CN and CC bond formation

CH bond functionalization for CN and CC bond formations via cross-dehydrogenative coupling (CDC) of N-allylbenzamides with indole as amine source has been developed under a copper-catalyzed condition. To the best of our knowledge, these are the first examples in which different classes of N-containing compounds were directly prepared from the readily available N-allylbenzamides using an inexpensive catalyst-oxidant (CuSO₄/TBHP) system. Further, it was applied for the synthesis of α-substituted N-allylbenzamides by using Grignard reagent as nucleophiles.     

Metal-free, organocatalytic cascade formation of C-N and C-O bonds through dual sp3 C-H activation: oxidative synthesis of oxazole derivatives

An organocatalytic cascade reaction that involves the formation of C-N, C-O and C=N bonds in one process via dual sp(3) C-H activation has been developed. This protocol affords a facile metal-free methodology for the synthesis of oxazole derivatives in air under mild conditions.     

Radical deoxygenation of alcohols and intermolecular carbon-carbon bond formation with surfactant-type radical chain carriers in water

An efficient and mild method is developed for radical deoxygenation of alcohols and formation of carbon-carbon bonds in water without adding additives such as surfactants. The reaction was applied to synthesis of 2′,3′-didehydro-2′,3′-dideoxynucleosides that are potent anti-HIV agents. The reaction afforded environmentally benign reaction conditions.     

C-C bond formation with carbon dioxide promoted by a silver catalyst

A catalytic amount of silver benzoate with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) was an effective catalytic system for the reaction of carbon dioxide with various ketones containing an alkyne group at an appropriate position. These reactions afforded the corresponding γ-lactone derivatives in good to high yields under mild conditions.     

Metal-free direct oxidative intermolecular diarylation of anilides at ambient temperature assisted by cascade selective formation of C-C and C-N bonds

A new atom-economical process of direct oxidative intermolecular functionalization of aniline derivatives by simple arenes was developed. The products were formed in a highly regioselective manner under metal-free conditions at ambient temperature.     

Fe(ClO4)3·×H2O-Catalyzed direct C-C bond forming reactions between secondary benzylic alcohols with different types of nucleophiles

A mild and efficient Fe(ClO₄)₃·×H₂O-catalyzed direct C-C bond coupling reactions of 1,3-dicarbonyl compounds, electron-rich arenes and heteroarenes and 4-hydroxycoumarin with secondary benzylic alcohols have been described. The benzylation of electron-rich arenes and heteroarenes leads to the synthesis of bis-symmetrical triarylmethanes. The present method is also applied to synthesis of an anti-coagulant compound, 4-hydroxy-3-(1,2,3,4-tetrahydronaphthalen-1-yl)-2H-chromen-2-one (Coumatetralyl (B)) from commercially available substrates was obtained in 85% yield. The advantages of this protocol are broad scope, mild conditions, use of inexpensive catalyst and simplicity of operation since water is the only side product.