Natural scaffolds-inspired synthesis of CF3-substituted macrolides enabled by Rh-catalyzed C–H alkylation macrocyclization

The development of innovative strategies and methods to provide natural product-like macrocycles not accessible by biosynthesis, but endowed with novel bioactivities and simplified structure, is highly desirable. Inspired by the key scaffolds of rapamycin and FR252921, herein, we report a Rh（III）-catalyzed C–H alkylation macrocyclization, which enables access to CF3-substituted macrolides. DFT calculations reveal that the chemoselectivity between C–H alkylation and olefination macrocyclization w...     

Palladium-catalyzed relay C–H functionalization to construct novel hybrid-arylcyclophosphorus ligand precursors

A new relay C–H functionalization of di([1,1’-biphenyl]-2-yl)phosphine oxide to obtain esterified and hydroxylated products with different hypervalent iodines as oxidants under palladium catalysis is disclosed.This reaction provides a more effective and concise strategy for the synthesis of novel structural hybrid-arylcyclophosphorus ligand precursors with a wide range of substrates and good functional group tolerance.     

Free amino group-directed C(sp2)–H arylation of α-amino-β-aryl esters by palladium catalysis

Native amino-directed palladium-catalyzed C(sp³)–H activation/functionalization has been developed for modification of α-amino acids and peptides. Herein a palladium(Ⅱ)-catalyzed C(sp²)–H arylation of α-amino-β-aryl esters has been disclosed, using the native amino as the directing group. A variety of chiralα-amino-β-aryl esters can be functionalized to give the corresponding ortho-substituted mono-and diarylated products.     

Synthesis of N-benzothiazol-2-yl-amides by Pd-catalyzed C(sp~2)–H functionalization

A catalytic synthesis of N-benzothiazol-2-yl-amides from 1-acyl-3-(phenyl)thioureas was achieved in the presence of a palladium catalyst through the C(sp2)–H functionalization/C–S bond formation. This synthetic methodology can produce various N-benzothiazol-2-yl-amides in high yields with good functional group tolerance.     

Transformations of N-arylpropiolamides to indoline-2,3-diones and acids via C≡C triple bond oxidative cleavage and C(sp^2)–H functionalization

A new palladium-catalyzed oxidative conversion of N-arylpropiolamides and H2O to various indoline-2,3-diones and acids through the C≡C triple bond cleavage and C(sp2)–H functionalization is described,which is promoted by a cooperative action of catalytic CuBr2,2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO)and O2.The method provides a practical tool for transformations of alkynes by means of a C–H functionalization strategy,which enables the formation of one C–C bond and multiple C–O bonds in a single reaction with high substrates compatibility and excellent functional group tolerance.     

Rhodium catalyzed regioselective arene homologation of aryl urea via double C–H bond activation and migratory insertion of alkyne

A convenient rhodium catalyzed oxidative arene homologation of aniline derivatives with symmetrical or unsymmetrical alkynes using Cu(OAc)_2 as oxidant is described. Urea group is shown to be effective as a directing group for initial ortho C–H activation. Two migratory insertion events of alkyne into Rh–C bond occur successively, both with complete regioselectivity. This method is particularly useful for synthesis of polyarenes with different substituents, which has not been reported with conventional protocol. A mechanism has been proposed to explain the observed data.     

Oxidation-induced ortho-selective C–H bond functionalization of 2-naphthylamine derivative

Selective C–H bond functionalization has been emerged as a versatile strategy for the construction of new chemical bonds. In the past decades, the directing group(DG)-assisted C–H bond activation has been developed as one of the most efficient methods for selective C–H functionalization. Although a great progress has been made by utilizing this traditional method, developing new strategy for selective C–H bond functionalization is still highly demanded. Hence, a novel oxidation-induced C–H bond functionalization method was demonstrated in this work. By this new method, ortho-C(sp2)–H chlorination of N-substituted 2-naphthylamine was realized in a highly selective manner.     

Efficient synthesis of 2-arylquinazolines via copper-catalyzed dual oxidative benzylic C–H aminations of methylarenes

A novel copper-catalyzed dual oxidative benzylic C–H aminations of methylarenes with 2-aminobenzoketones in the presence of ammonium acetate was developed. This reaction represents a new avenue for 2-arylquinazolines with good yields. A key intermediate was detected and the kinetics isotope effect(KIE) indicated that C–H bond cleavage was the rate-determining step.     

Copper catalyzed/mediated direct B–H alkenylation/alkynylation in carboranes

Base metal catalyzed regioselective cage B–H functionalization has been achieved. Under the assistance of a bidentate directing group, Cu-catalyzed [4+2] annulation of carboranyl amides with internal alkynes affords unprecedented C,B-substituted carborane-fused-pyridone derivatives, whereas the use of terminal alkynes leads to B–H/C(sp)–H dehydrocoupling products. The isolation and structural identification of a notably stable Cu(Ⅰ) intermediate shed light on the reaction mechanism, which is proposed to involve a Cu(Ⅲ) intermediate.     

C–H Arylation using acyl thiourea ligands: Applications in the synthesis of 3,6-diaryl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles

Synthesis of a series of new 3,6-diaryl-[1,2,4]triazolo[3,4-b] [1,3,4]thiadiazoles(5a–o) was achieved by phophine free, C–H arylative cross-coupling of 6-aryl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles(4a–o)with suitably substituted iodoanilines using 1-(2-naphthoyl)-3-(4-bromophenyl)thiourea as a ligand.The requisite triazolothiadiazoles(4a–o) were obtained by the condensation of 4-amino-1,2,4-triazole-3-thiol(3) with suitably substituted aromatic acids in the presence of phosphoryl chloride.     

Aromatic and olefinic C–H alkenylation by catalysis with spirocyclic NHC Ru(Ⅳ) pincer complex

Catalyst innovation lies at the heart of transition-metal-catalyzed reaction development. In this article, we have explored the C(sp²)–H alkenylation activity with novel spirocyclic N-heterocyclic carbene(NHC)-based cyclometalated ruthenium pincer catalyst system, SNRu-X. After screening catalyst and condition, a high valent Ru(Ⅳ) dioxide(X = O₂) species has demonstrated superior reactivity in the catalytic alkenylation of aromatic and olefinic C–H bonds with unactivated al...     

Neutral C–H bond vs. electron pair of N(sp~2): A binding site effect study of macrocycle anion receptor

To evaluate the effect of neutral C–H bond or electron pair of nitrogen atom with sp2hybridization(N(sp2)) involving into the same chemical environment for anion binding, two analogous tetracationic imidazolium macrocycles, namely cyclo[2](2,6-bis-(1H-imidazol-1-yl)pyridine) [2](1,3-dimethylenebenzene)(14+), and cyclo[2](2,6-bis-(1H-imidazol-1-yl)pyridine)[2](2,6-di methylenepyridine)(24+)were studied in detail as small inorganic anion receptors. The guest anions with different shapes are Cl,N3, NO3, and H2PO4. The host–guest interactions were characterized via1 H NMR spectroscopy,electrospray ionization mass spectrometry(ESI-MS) and single crystal X-ray crystallography. The results implied that macrocyclic hosts with similar backbone but two distinct binding sites(14+with neutral C–H vs. 24+with N(sp2)) vary markedly in their response to anions, including the binding modes and association constants. The finding will serve to the construction of new anion receptors, even improve insights into the anion binding process in biology.     

A theoretical study on the mechanisms of intermolecular hydroacylation of aldehyde catalyzed by neutral and cationic rhodium complexes

In this paper, we used density functional theory(DFT) computations to study the mechanisms of the hydroacylation reaction of an aldehyde with an alkene catalyzed by Wilkinson's catalyst and an organic catalyst 2-amino-3-picoline in cationic and neutral systems. An aldehyde's hydroacylation includes three stages: the C–H activation to form rhodium hydride(stage I), the alkene insertion into the Rh–H bond to give the Rh-alkyl complex(stage II), and the C–C bond formation(stage III). Possible pathways for the hydroacylation originated from the trans and cis isomers of the catalytic cycle. In this paper, we discussed the neutral and cationic pathways. The rate-determining step is the C–H activation step in neutral system but the reductive elimination step in the cationic system. Meanwhile, the alkyl group migration-phosphine ligand coordination pathway is more favorable than the phosphine ligand coordination-alkyl group migration pathway in the C–C formation stage. Furthermore, the calculated results imply that an electron-withdrawing group may decrease the energy barrier of the C–H activation in the benzaldehyde hydroacylation.     

Unactivated C(sp3)–H functionalization via vinyl cations

Direct functionalization of inert C(sp³)–H bonds is a topic of immense contemporary interest and exceptional value in organic synthesis.The recent research has established a novel and practical protocol which features the engagement of vinyl cation species to functionalize C(sp³)–H bonds.The discussion of the topic is arranged by the strategies to generate the reactive intermediates,including ionization of vinyl triflates,addition of electrophiles to alkynes,tandem cyclization of enynes or diynes,and decomposition ofβ-hydroxy-α-diazo ketones.This review closes with a personal perspective on the dynamic research area of unactivated C(sp³)–H functionalization via vinyl cations.Hopefully,it will provide timely illumination and beneficial guidance for organic chemists who are interested in this area.Meanwhile continued development of the field is strongly anticipated in the future.     

Cu(Ⅱ)-catalyzed domino reaction of 2-halobenzamide and arylmethanamine to construct 2-aryl quinazolinone

A novel method for achieving a copper(II)-catalyzed domino reaction for the construction of 2-aryl quinazolinones,without the addition of any ligand and additive,has been developed.The domino reaction achieved N-(a-substituted)benzylation,benzylic C–H amidation,and C–C(or C–H) bond cleavage.     

Copper-catalyzed enantioselective cyanation of benzylic C–H bonds via radical relay

正Direct methods that enable stereoselective functionalization of C(sp~3)–H bonds could facilitate efficient preparation of therapeutics and agrochemicals,and shall have a major effect on the discovery and development of new pharmaceuticals.Although the transformations through C(sp~2)–H bond cleavage have been significantly developed in the past decades,the direct C(sp~3)–H functionalization,especially the asymmetric transformation is still a big challenge.Demon-     

Palladium-catalyzed oxidative cyclopropanation of enamides and norbornenes initiated by C–H activation

A novel palladium-catalyzed oxidative cyclopropanation of enamides and norbornenes has been developed. The reaction proceeded through palladium-catalyzed vinyl C–H bond activation of enamides followed by two migratory insertions, β-(N)H elimination and hydrolyzation cascade steps. The reaction tolerates a range of functional groups and provides an effective method for the synthesis of cyclopropane-fused norbornanes in good yields under mild conditions.     

Regioselective introduction of vinyl trifluoromethylthioether to remote unactivated C(sp~3)–H bonds via radical translocation cascade

Described herein is an efficient protocol for the regioselective introduction of a vinyl trifluoromethylthioether to remote unactivated C(sp~3)–H bonds. The cascade process involves the vinyl radical-mediated 1,5-hydrogen atom transfer(HAT) and remote vinyl migration. During the transformation, inert C–H and C–C bonds are consecutively cleaved under mild conditions.The reaction features good functional group tolerance, broad substrate scope, and high regio-/stereo-selectivity.     

C–H alkylation of pyridines with olefins catalyzed by imidazolin-2-iminato-ligated rare-earth alkyl complexes

An array of rare-earth bis(aminobenzyl) complexes supported by imidazolin-2-iminato ligands were synthesized and structurally characterized. These complexes showed high activity towards ortho-Csp²–H alkylation of 2-alkylpyridines and benzylic Csp³–H alkylation of 2,6-dialkylpyridines with alkenes. A wide range of alkyl or aryl substituted olefin substrates are compatible,providing an atom-economical route to linear or branched alkylated pyridine derivatives in moderate to h...     

Electrospinning of GeO_2–C fibers and electrochemical application in lithium-ion batteries

GeO_2–C fibers were successfully synthesized using electrospinning homogeneous sol and subsequent calcination in an inert atmosphere. The spinnable sol was prepared by adding polyacrylonitrile(PAN)and polyvinylpyrrolidone(PVP) in a weight ratio of 1:1 into a mixture with white precipitate produced by dropping GeCl_4 into DMF. X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TGA), scanning electron microscopy(SEM) and transmission electron microscopy(TEM) were employed to characterize the as-obtained fibers, and electrochemical tests were conducted to measure electrochemical performance of the electrode. The electrospun fibers have uniform diameters of 300 nm. After being calcined at 600 8C for 2 h in Ar, they transform to amorphous GeO_2–C fibers with the same morphologies. The Ge O_2–C fibers exhibit excellent cycling stability with a high reversible capacity of 838.93 m A h g~(-1)after 100 cycles at a current density of 50 m A g~(-1), indicating the composite fibers could be promising anode candidates for lithium-ion batteries.