Rh(III)-catalyzed, 1,2,3-triazole-assisted directed CH coupling with diazo diphosphonates

A mild and efficient procedure was developed for the [Cp1Rh(III)]-catalyzed, 1,2,3-triazole directed CH coupling with diazomethylene-diphosphonates. This protocol provided a step- and atom-economical protocol for CC bond formation and led to structurally diverse 2-(1,2,3-triazol-2-yl)benzyl diphosphonates in good to excellent yields.     

Photocatalytic anion oxidation achieves direct aerobic difunctionalization of alkenes leading to β-thiocyanato alcohols

A novel visible light-driven oxidative cascade reaction for the synthesis of β-thiocyanato alcohols via difunctionalization of alkenes is described for the first time. In this protocol inorganic ion thiocyanate was successfully converted into radical through photocatalysis by employing Rose Bengal as a photocatalyst to mediate the single-electron transfer. This hydroxylation process did not need extra reducing agent and the new CS and CO bonds could be constructed in one pot. Molecular oxygen not only was used as an excellent terminal oxidant, but also served as a green oxygen source, which is one of the most ideal processes to realize CH bond oxidation functionalization. Moreover, the reaction also proceeded very well under irradiation of sunlight.     

Recent advance in radical fluoroalkylation with sulfinate salts

In the last few years, the incorporation of a fluoroalkyl moiety into an organic molecule has been extensively studied. Especially, radical fluoroalkylation, involving the formation of CC and Cheteroatom bonds, presents its valuable synthetic potential to achieve fluoroalkylated compounds. This digest paper highlights recent progress on fluoroalkylation with sulfinate salts, and focuses on radical tri-/di-/monofluoromethylation during the last five years.     

Influence of sulfur groups on carboxylic acid strengths

The relative acid strength for a series of monocarboxylic acids of the general formula RX(CH₂)_nCOOH and related dicarboxylic acids of the general formula HOOC(CH₂)_nX(CH₂)_nCOOH, where R?=?Ph or Me, X?=?CH₂, S, SO, or SO₂; and n?=?1 or 2 as appropriate; have been studied as a function of X. It is found that sulfur containing acids have lower pKa values than the corresponding carbon analogues, that the pK_a is highest for the thioacids and lowest for the sulfonyl acids, that the pK_as increase as n increases, and that for the dicarboxylic acid systems only the thio members show a significant reduction in pK_a (2) – pK_a (1) differences upon changing n from 1 to 2.     

Investigation on sensing mechanism of a fluorescent probe for TNP detection in aqueous solution

In this paper, the synthesis and spectral properties of a fluorescent probe Nph-An for TNP detection has been introduced and its sensing mechanism has been studied with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. For TNP detection in aqueous solution the probe shows high sensitivity, selectivity and efficiency. The theoretical results demonstrate that the excited-state intermolecular hydrogen bonding (HB) plays an important role for the TNP detection. In the excited state, the intermolecular HB between Nph-An and TNP is strengthened, and thus strongly facilitates the nonirradiative PET process to induce the fluorescence quenching. Whereas, the probe Nph-An emits strong fluorescence because of the intramolecular charge transfer (ICT) properties, which is confirmed by the solvatochromism effect. The calculated absorption spectra of Nph-An and Nph-An + TNP agree well with the experimental values and theoretical analysis provides a detailed and clear explanation of the sensing mechanism.     

One-pot synthesis of [1,2,4]Triazolo[1,5-a]pyridines from azines and benzylidenemalononitriles via copper-catalyzed tandem cyclization

A simple and efficient copper-catalyzed tandem radical cyclization reaction has been discovered for the synthesis of triaryl [1,2,4]triazolo[1,5-a]pyridines from easily accessible azines and benzylidenmalononitriles. The new transformation involves multiple CH/CC bonds cleavage and CC/CN bonds formation, with extrusion of gaseous hydrogen and methane. A wide variety of substrates with different functional groups could be converted into the corresponding products in good yields. The fused heterocycles have strong blue fluorescence with large Strokes shifts and high quantum yields.     

Guanidine organocatalysis for enantioselective carbon-heteroatom bond-forming reactions

Guanidine-containing molecules have been employed as organocatalysts, and chiral guanidines have been widely explored as catalysts for mediating asymmetric reactions by constructing an asymmetric reaction environment. Currently, many guanidine-catalyzed asymmetric reactions are available, and some excellent reviews have appeared. In this Digest, we focused on recent progress in the guanidine-catalyzed asymmetric construction of CN, CO, CP, and CS bonds, especially developments since 2010.     

Formal synthesis of (±) —quebrachamine through regio- and stereoselective hydrocyanation of arylallene

This article describes the formal synthesis of quebrachamine based on regio- and stereoselective hydrocyanation of 1,3-disubstituted allenes. Allenyl CC double bonds are effectively discriminated through Ni-catalyzed hydrocyanation and a CN group is utilized as a synthon of piperidine ring. Several steps from HCN adduct afforded known intermediates to quebrachamine.     

The investigation on the NH reactivity of pentacoordinate spirophosphoranes by H/D exchange and NMR experiments

Different pentacoordinate spirophosphoranes were investigated by H/D exchange and NMR tracking experiments. The H/D exchanged site of spirophosphoranes was confirmed to be the NH bond instead of the PH bond according to the integration of the signal changes in proton-decoupled, proton-coupled ³¹P NMR and ¹H NMR tracking experiments. The reactivity of NH bond at the spiroring of spirophosphoranes was explored by the rate constant of H/D exchange of different spirophosphoranes. The results demonstrated that the reactivity of NH bond of spirophosphoranes was influenced by steric hindrance and the species of substituent at phosphorus atom, and the electronic effect of the substituent was the main effect factor on the reactivity of the NH bond. The strong electron-withdrawing group at phosphorus resulted in more reactive NH bond of spirophosphoranes. These results are beneficial to further understand and explore the characteristics of pentacoordinate spirophosphoranes.     

Recent topics in annulation reaction via double CH bond cleavage and double CC bond formation

Cyclic compounds have been consistently key components in organo functional molecules. To construct cycles, a catalytic two CH bond-cleaving annulation is one of the most ideal and straightforward methods with atom and step economies. Recently, many patterns of such annulation reactions have been developed, which construct a variety of cyclic compounds consisted of from simple to complex frameworks. This Digest focuses a recent progress in two or more than three CH bond-cleaving annulation reactions and is outlined as follows: (1) intramolecular annulation, (2) intermolecular annulation via double CH bond cleavages in one molecule, and (3) intermolecular annulation via double CH bond cleavages in two molecules.     

Copper-mediated Chan-Evans-Lam N-arylation of 5-methylene-4-aryl-1,5-dihydro-2H-pyrrol-2-one derivatives

A simple and efficient procedure for the synthesis of N-aryl 5-methylene-4-aryl-1,5-dihydro-2H-pyrrol-2-one derivatives has been developed through copper-mediated CN bond formation. The synthetic protocol allows for versatile and robust CN arylation with a range of readily available boronic acids under mild conditions.     

Visible-light-mediated cascade difunctionalization/cyclization of alkynoates with acyl chlorides for synthesis of 3-acylcoumarins

A new visible-light-mediated radical cyclization of alkynoates with acyl chlorides is described for the one-pot construction of diverse 3-acylcoumarins with high efficiency and selectivity. This method is successful by sequential difunctionalization of an alkynes CC triple bond with the CCl bonds of acyl chloride and aromatic C(sp²)H bonds. The cyclization is proposed to simultaneously form two new carbon–carbon bonds, and involves radical acylation, 5-exo-trig cyclization, and ester migration.     

Phosphinate selective hosts and importance of CH hydrogen bonding for affinity modulation toward anion guests

Even though phosphinate and its analogs are very important guests in nature, the artificial receptors which are capable of selective recognition of phosphinate are rare. Here, we report a series of acetate and phosphinate selective hosts (1, 2 and 3) which utilize amide NH and aliphatic CH groups as hydrogen bonding donors. In this series of receptors, even though the amide NH hydrogen bonding element was found to be the most significant, by varying the polarity of CH group, the magnitude of recognition could be modulated considerably. The affinities of host 3 against all the tested anion guests showed significantly higher affinities compared with those of hosts 1 and 2, and this could be attributed to the difference of CH group polarities among the receptors 1, 2 and 3. C_α-H hydrogen in host 3 is the most highly polarized by the charged pyridinium group. Therefore, it is the strongest host in this series of hosts. From the experiments shown here, we demonstrated the importance of CH hydrogen bonding element as a decisive modulating moiety for anionic recognition.     

Site selective [bmIm]OH catalyzed CC bond functionalization under green conditions

Effective methodology that activates selectively either end of a carbon–carbon triple bond requires key challenge of differentiating between the multitude of CC bonds present in complex organic molecule. The synthetic strategy exploited the electronic biases within the substrate and successfully achieved site–selective [bmIm]OH catalyzed CC bond functionalization under mild reaction conditions. This resulted in C-2-selective addition of phenacyl bromide on p-substituted phenyl acetylene and C-1 selective addition on the o-substituted phenyl acetylene leading to CC bond formation. The reaction proceeded smoothly with excellent yield under ambient conditions. This report demonstrates the progress on the catalytic activity of recyclable [bmIm]OH for selective CC bond formation.     

Concept of Ir-catalyzed CH bond activation/borylation by noncovalent interaction

Noncovalent interactions play a fundamental role in molecular biology, crystal engineering, supramolecular chemistry, drug design, sensing applications, and many other research fields in the chemical sciences. Because of this importance, thorough research efforts have been focused on the interpreting and quantifying these interactions, which include H-bonding, electrostatic effects, ππ interaction, cation-π interaction, hydrophobic-hydrophobic interaction, van der Waals forces, and other such type of interactions. However, on the synthetic standpoint, use of these noncovalent interactions are rare, although might be beneficial for the site-selective CH bond activation and functionalization by transition metal catalysis. In this context, iridium-catalyzed CH borylation has gained immense popularity due to the versatility conferred to the CB bonds. Very recently, researchers have started employing these interactions as a governing factor for attaining regioselectivity in arene CH borylation. In this perspective, we will focus on the advancements made so far by the use of various noncovalent interactions in Ir-catalyzed borylations.     

Selective,C-3 Friedel-Crafts acylation to generate functionally diverse,acetylated Imidazo[1,2-a]pyridine derivatives

Carbon-carbon bonds are integral for pharmaceutical discovery and development. Frequently, CC bond reactions utilize expensive catalyst/ligand combinations and/or are low yielding, which can increase time and expenditures in pharmaceutical development. To enhance CC bond formation protocols, we developed a highly efficient, selective, and combinatorially applicable Friedel-Crafts acylation to acetylate the C-3 position of imidazo[1,2-a]pyridines. The reaction, catalyzed by aluminum chloride, is both cost effective and more combinatorial friendly compared to acetylation reactions requiring multiple, stoichiometric equivalents of AlCl₃. The protocol has broad application in the construction of acetylated imidazo[1,2-a]pyridines with an extensive substrate scope. All starting materials are common and the reaction requires inexpensive, conventional heating methods for adaptation in any laboratory. Further, the synthesized compounds are predicted to possess GABA activity through a validated, GABA binding model. The developed method serves as a superior route to generate C-3 acetylated imidazo[1,2-a]pyridine building-blocks for combinatorial synthetic efforts.     

Rhodium-catalyzed NH-indole-directed ortho CH coupling of 2-arylindoles with diazo compounds via metal carbene migratory insertion

A high regioselective rhodium-catalyzed ortho CH coupling of 2-arylindoles with diazo compounds via NH-indole-directed CH bond activation has been developed. The catalytic reaction features mild reaction conditions, broad substrate scope and good functional group tolerability.     

Total synthesis of lithospermic acid using Fe-catalyzed Cross-Dehydrogenative-Coupling reaction and Pd-catalyzed ester-directed CH olefination

The total synthesis of lithospermic acid has been accomplished employing two CH activation reactions as key steps. Fe-catalyzed Cross-Dehydrogenative-Coupling reaction was used for the rapid construction of benzofuran framework. Pd-catalyzed ester-directed CH olefination allowed the efficient assembly of the dihydrobenzofuran ester and acrylate moieties.     

[1,2,5]Oxadiazolo[3,4-d]pyridazine 1,5,6-trioxides: efficient synthesis via the reaction of 3,4-bis(hydroxyimino)methyl)-1,2,5-oxadiazole 2-oxides with a mixture of concentrated nitric and trifluoroacetic acids and structural characterization

An efficient synthesis of [1,2,5]oxadiazolo[3,4-d]pyridazine 1,5,6-trioxides (1) from 3,4-bis(hydroxyimino)methyl)-1,2,5-oxadiazole 2-oxides using a mixture of concentrated nitric and trifluoroacetic acids has been developed. The scope of the unconventional reaction was established. The 4,7-dinitro[1,2,5]oxadiazolo[3,4-d]pyridazine 1,5,6-trioxide 1f represents a new high energy compound, unfortunately with low thermal stability. The parent [1,2,5]oxadiazolo[3,4-d]pyridazine 1,5,6-trioxide 1c was studied by single-crystal X-ray diffraction analysis which revealed a planar molecule with an unusually long intracyclic NN bond of 1.668(5)?Å and unexpected exo-cyclic bond angles at the nitroxyl nitrogen atoms. In the crystal, the molecules of 1c are bound to each other by strong π-π stacking and CH?O hydrogen bonding interactions into a three-dimensional framework that results in a high crystal density of 1.833?gcm^?3.     

Perturbation par l''oxygene de l''oxydation anodique De l''anion complexe cr(co)5cn

OsCl₂(CFCl)(CO)(PPh₃)₂ results from reaction between OsCl₂(CCl₂)(CO)(PPh₃)₂ and Cd(CF₃)₂(DME). The CFCl ligand is converted into CFNMe₂ and CFSEt ligands through reaction with Me₂NH and NaSEt, respectively. The crystal structure of RuCl₂(CFOCH₂CMe₃)(CO)(PPh₃)₂ reveals the following dimensions about the carbene-carbon atom: RuC, 1.914(5)Å; CO, 1.303(7)Å; CF, 1.307(6)Å; RuCF, 127.1(4)°; RuCO, 125.5(4)°; FCO, 107.4(5)°.