Cobalt-catalyzed oxidative esterification of allylic/benzylic C(sp3)–H bonds

A protocol for the cobalt-catalyzed oxidative esterification of allylic/benzylic C(sp³)–H bonds with carboxylic acids was developed in this work. Mechanistic studies revealed that C(sp³)–H bond activation in the hydrocarbon was the turnover-limiting step and the in-situ formed [Co(III)]Ot-Bu did not engage in hydrogen atom abstraction (HAA) of a C–H bond. This protocol was successfully incorporated into a synthetic pathway to β-damascenone that avoided the use of NBS.     

Photoredox-catalyzed C(sp2)–N coupling reactions

Photoredox-catalyzed radical reactions have attracted intense interest from synthetic chemists over the past several years. The photoredox-catalyzed C(sp²)–N coupling reactions, including Ullmann type C–N coupling (C–X/N–H type coupling), redox neutral C–N coupling (C–H/N–X type coupling) and oxidative C–N coupling (C–H/N–H type coupling), have been summarized in this digest.     

Cobalt(II)-Catalyzed C(sp3)−C(sp3) Coupling for the Direct Stereoselective Synthesis of 2-Deoxy-C-Glycosides from Glycals

We report a ligand-controlled Co^II-catalyzed C(sp³)−C(sp³) coupling hydroalkylation for direct and β-selective synthesis of 2-deoxy-C-glycosides from glycals. This reaction proceeds by a radical pathway for alkyl halide activation and is β-selective through ligand control. This approach may inspire the development of further stereoselective coupling reactions with potential application in the field of carbohydrates.     

Asymmetric Organocatalytic Direct C(sp2)?H/C(sp3)?H Oxidative Cross‐Coupling by Chiral Iodine Reagents

An asymmetric organocatalytic direct C H/C H oxidative coupling reaction of N¹,N³‐diphenylmalonamides has been well established by using chiral organoiodine compounds as catalysts, wherein four C H bonds were stereoselectively functionalized to give structurally diverse spirooxindoles with high levels of enantioselectivity. More importantly, the findings indicated that chiral hypervalent organoiodine reagents can serve as alternative catalysts for the creation of enantioselective functionalization of inactive C H bonds.     

Iron-catalyzed alkenylation of cyclic ethers via decarboxylative sp(C)–sp(C) coupling

An efficient Fe(acac)₃-catalyzed decarboxylative C(sp²)–C(sp³) coupling reaction via oxidation of C–H bond adjacent to an oxygen atom has been developed successfully, in which cyclic ethers are selectively transformed into the corresponding alkenylation products with good chemical yields and excellent stereoselectivities. The mechanism was studied and the reaction was supposed to proceed through a radical oxidative coupling process.     

DDQ-mediated direct oxidative coupling of amides with benzylic and allylic sp3 C–H bonds under metal-free conditions

A simple and efficient method for the direct oxidative coupling of amides with benzylic and allylic sp³ C–H bonds using DDQ as an oxidant is described. A range of amides including benzamide, benzyl carbamate, and substituted sulfonamides reacted efficiently with various benzylic and allylic substrates under metal free conditions to afford amidation products in good to excellent yields.     

Polystyrene-supported cu(II)-R-Box as recyclable catalyst in asymmetric Friedel–Crafts reaction

The complex of copper(II) trifluoromethanesulfonate with chiral isopropyl bis(oxazoline) ligand (i-Pr-Box) was immobilized on accessible and inexpensive Merrifield resin according to a “click” procedure. The resulting catalyst showed high efficiency and recyclability in the asymmetric Friedel–Crafts alkylation of indole and its derivatives. The catalyst can be recycled five times without appreciable loss in activity and enantioselectivity.     

Cl2⋅− Mediates Direct and Selective Conversion of Inert C(sp3)−H Bonds into Aldehydes/Ketones

Developing new reactive pathway to activate inert C(sp³)−H bonds for valuable oxygenated products remains a challenge. We prepared a series of triazine conjugated organic polymers to photoactivate C−H into aldehyde/ketone via O₂→H₂O₂→⋅OH→Cl⋅→Cl₂⋅⁻. Experiment results showed Cl₂⋅⁻ could successively activate C(sp³)−H more effectively than Cl⋅ to generate unstable dichlorinated intermediates, increasing the kinetic rate ratio of dichlorination to monochlorination by a factor of 2,000 and thus breaking traditional dichlorination kinetic constraints. These active intermediates were hydrolyzed into aldehydes or ketones easily, when compared with typical stable dichlorinated complexes, avoiding chlorinated by-product generation. Moreover, an integrated two-phase system in an acid solution strengthened the Cl₂⋅⁻ mediated process and inhibited product overoxidation, where the conversion rate of toluene reached 16.94 mmol/g/h and the selectivity of benzaldehyde was 99.5 %. This work presents a facile and efficient approach for selective conversion of inert C(sp³)−H bonds using Cl₂⋅⁻.     

Revealing Silylation of C(sp2)/C(sp3)–H Bonds in Arylphosphines by Ruthenium Catalysis

The first aromatic C−H silylation between arylphosphines and hydrosilanes enabled by a ruthenium complex has been developed. The excellent ortho-selectivity results from a four-membered metallacyclic intermediate involving phosphorus chelation. The developed system can be extended to the benzylic C−H silylation of arylphosphines. Diverse silylated arylphosphines are produced, exhibiting broad functional group compatibility. Further functionalization of the products under mild conditions renders the formed compounds useful building blocks.     

A Cu/Cinchona P,N-ligand system enabled general asymmetric C(sp~3)–C(sp) coupling

正Due to the special structural feature and versatile reactivity towards various types of transformations, alkynes have inspired continuous research interest for their generation, incorporation and application in organic synthesis, chemical biology and material science [1]. Notably, since its invention in 1975, the Sonogashira reaction, which efficiently couples aryl halides with aryl or vinyl terminal alkynes via Pd(0)/Cu(I) synergistic catalysis, has proven to be one of the most     

镍催化构筑C(sp3)—C(sp3)键反应研究进展

过渡金属催化的偶联反应是构筑C-C键的高效方法,在有机合成中得到了广泛的应用.然而,相对于Heck反应、Negishi偶联与Suzuki偶联等构筑C（sp²）-C（sp²）键的反应,过渡金属催化的构筑C（sp³）-C（sp³）键的偶联反应较难进行,发展较晚.近年来,烷基-烷基C-C键偶联反应受到广泛的重视,一些高效催化剂被开发出来,其中镍催化剂展示出独特的催化活性和选择性.本文将综述镍催化烷基-烷基C-C键偶联反应最新研究进展,主要包括烷基亲电试剂与金属有机试剂交叉偶联反应、导向基参与的C（sp³）-H键活化的偶联反应、镍-光反应催化剂协同催化偶联反应、烷基亲电试剂与亲电试剂的还原偶联反应和镍催化烯烃加成反应等.     

Stereoselective C(sp3)-C(sp2) Negishi coupling of (2-amido-1-phenylpropyl)zinc compounds through the steric control of β-amido group

A controllable diastereoselective C(sp2)-C(sp3) Negishi coupling reaction of secondary benzylic zinc reagents with aryl bromides has been demonstrated for the first time, forming medicinally important 1-arylphenylethylamines. In the presence of Pd(OAc) 2 and S-phos, open-chain (2-amido-1-phenylethyl)zinc reagents bearing a -NHAc or NHCHO group underwent cross-coupling reaction to give syn 1-arylphenylethylamine as the major products, whereas the zinc reagents bearing a sterically hindered-NHCOC(CH3)2 OTBS group specifically yielded anti 1-arylphenylethylamines.     

Dynamically biased statistical model for the ortho/para conversion in the H(2)+H(3) (+) → H(3) (+)+ H(2) reaction

In this work we present a dynamically biased statistical model to describe the evolution of the title reaction from statistical to a more direct mechanism, using quasi-classical trajectories (QCT). The method is based on the one previously proposed by Park and Light [J. Chem. Phys. 126, 044305 (2007)]. A recent global potential energy surface is used here to calculate the capture probabilities, instead of the long-range ion-induced dipole interactions. The dynamical constraints are introduced by considering a scrambling matrix which depends on energy and determine the probability of the identity/hop/exchange mechanisms. These probabilities are calculated using QCT. It is found that the high zero-point energy of the fragments is transferred to the rest of the degrees of freedom, what shortens the lifetime of H(5) (+) complexes and, as a consequence, the exchange mechanism is produced with lower proportion. The zero-point energy (ZPE) is not properly described in quasi-classical trajectory calculations and an approximation is done in which the initial ZPE of the reactants is reduced in QCT calculations to obtain a new ZPE-biased scrambling matrix. This reduction of the ZPE is explained by the need of correcting the pure classical level number of the H(5) (+) complex, as done in classical simulations of unimolecular processes and to get equivalent quantum and classical rate constants using Rice-Ramsperger-Kassel-Marcus theory. This matrix allows to obtain a ratio of hop/exchange mechanisms, α(T), in rather good agreement with recent experimental results by Crabtree et al. [J. Chem. Phys. 134, 194311 (2011)] at room temperature. At lower temperatures, however, the present simulations predict too high ratios because the biased scrambling matrix is not statistical enough. This demonstrates the importance of applying quantum methods to simulate this reaction at the low temperatures of astrophysical interest.     

Pd(II)-catalyzed cascade Heck/intramolecular C(sp2)–H amidation reaction: An efficient route to 4-aryl-2-quinolinones

A Pd(II)-catalyzed cascade Heck/intramolecular C(sp²)–H amidation reaction is described for the synthesis of 4-aryl-2-quinolinone derivatives. Substituted cinnamamide containing 2-(pyridin-2-yl)ethanamine unit reacts with aryl iodide to form intermediate by Heck reaction. Then, the intermediate takes place intramolecular amidation via C(sp²)–H activated process promoted by orientation group.     

Magnetic Cu–Schiff base complex with an ionic tail as a recyclable bifunctional catalyst for base/Pd-free Sonogashira coupling reaction

Journal of the Iranian Chemical Society - A Cu(II)–Schiff base complex containing imidazolium ionic phase was prepared and decorated on γ-Fe2O3 magnetic nanoparticles...     

Efficient and Direct Functionalization of Allylic sp3 C−H Bonds with Concomitant CO2 Reduction

Solar-driven CO₂ reduction integrated with C−C/C−X bond-forming organic synthesis represents a substantially untapped opportunity to simultaneously tackle carbon neutrality and create an atom-/redox-economical chemical synthesis. Herein, we demonstrate the first cooperative photoredox catalysis of efficient and tunable CO₂ reduction to syngas, paired with direct alkylation/arylation of unactivated allylic sp³ C−H bonds for accessing allylic C−C products, over SiO₂-supported single Ni atoms-decorated CdS quantum dots (QDs). Our protocol not only bypasses additional oxidant/reductant and pre-functionalization of organic substrates, affording a broad of allylic C−C products with moderate to excellent yields, but also produces syngas with tunable CO/H₂ ratios (1 : 2–5 : 1). Such win-win coupling catalysis highlights the high atom-, step- and redox-economy, and good durability, illuminating the tantalizing possibility of a renewable sunlight-driven chemical feedstocks manufacturing industry.     

Ligand-Enabled [3+2] Annulation of Aromatic Acids with Maleimides by C(sp3)−H and C(sp2)−H Bond Activation

A palladium-catalyzed [3+2] annulation of substituted benzoic acids with maleimides leading to tricyclic heterocyclic molecules having a free carboxylic group in a high atom- and step-economical manner is described. The reaction proceeds via a dual C−H bond activation such as C(sp³)−H at the benzylic position and C(sp²)−H bond activation at the meta position of substituted aromatics. An external ligand (MPAA) is crucial for the success of present protocol. Further, the decarboxylation and esterification of the free carboxylic acid group of observed products were carried out.