Unprecedented Transformation of a Directing Group Generated In Situ and Its Application in the One‐Pot Synthesis of 2‐Alkenyl Benzonitriles

An unprecedented protocol for the transformation of benzoyl azides into benzonitrile derivatives via iminophosphoranes generated in situ is described. The strategy was successfully applied to the de‐novo synthesis of 2‐alkenylated benzonitrile derivatives from benzoyl azides through ortho C?H activation/alkenylation followed by subsequent rearrangement. The salient features of this protocol involve incorporation of two important functionalities through cyanation and olefination in one pot under mild reaction conditions by using a less expensive Ru catalyst. The mechanism was established by isolating and characterising (using ³¹P NMR) an intermediate with two ortho functionalities, iminophosphorane and olefin, under specific reaction conditions.     

Oxidative Olefination of Anilides with Unactivated Alkenes Catalyzed by an (Electron‐Deficient η5‐Cyclopentadienyl)Rhodium(III) Complex Under Ambient Conditions

The oxidative olefination of sp² C?H bonds of anilides with both activated and unactivated alkenes using an (electron‐deficient η⁵‐cyclopentadienyl)rhodium(III) complex is reported. In contrast to reactions using this electron‐deficient rhodium(III) catalyst, [Cp*RhCl₂]₂ showed no activity against olefination with unactivated alkenes. In addition, the deuterium kinetic isotope effect (DKIE) study revealed that the C?H bond cleavage step is thought to be the turnover‐limiting step.     

Olefin Cross‐Metathesis: Studies towards the Total Synthesis of (+)‐Bitungolide F

A stereoselective synthesis of (5S,6S)‐6‐[(2S,5S,7R,8E,10E)‐5‐(benzyloxy)‐7‐{[(tert‐butyl)dimethylsilyl]oxy}‐11‐phenylundeca‐8,10‐dien‐2‐yl]‐5‐ethyl‐5,6‐dihydro‐2H‐pyran‐2‐one (=(+)‐9‐O‐benzyl‐11‐O‐[(tert‐butyl)dimethylsilyl]bitungolide F) is reported. The strategy involves Gilman reaction, olefin cross‐metathesis, and Horner? Wadsworth? Emmons olefination as key steps.     

Palladium(II)‐Catalyzed meta‐CH Olefination: Constructing Multisubstituted Arenes through Homo‐Diolefination and Sequential Hetero‐Diolefination

Divinylbenzene derivatives represent an important class of molecular building blocks in organic chemistry and materials science. Reported herein is the palladium‐catalyzed synthesis of divinylbenzenes by meta‐C? H olefination of sulfone‐based arenes. Successful sequential olefinations in a position‐selective manner provided a novel route for the synthesis of hetero‐dialkenylated products, which are difficult to access using conventional methods. Additionally, 1,3,5‐trialkenylated compounds can be generated upon successful removal of the directing group.     

A Stereoselective Total Synthesis of Decarestrictine I

A convergent and stereoselective total synthesis of decarestrictine I, a polyketide natural product, is described. Both acid and alcohol fragments were prepared from the readily available L ‐malic acid via Still? Gennari olefination and Sharpless asymmetric epoxidation. The Steglich esterification and ring‐closing metathesis (RCM) are employed to combine both acid and alcohol fragments.     

Palladium‐Catalyzed Oxidative Cross‐Coupling of α‐Cyanoketene Dithioacetals with Olefins

Efficient palladium‐catalyzed cross‐coupling reactions of the internal olefins α‐cyanoketene dithioacetals with a variety of olefins were achieved in dioxane/HOAc/DMSO (9:3:1 v/v/v) under air atmosphere or by means of AgOAc as the terminal oxidant. Electron‐deficient terminal olefins reacted to form the linear diene derivatives with air as the oxidant. Styrenes underwent the cross‐coupling to give both the linear and branched dienes when using AgOAc as the oxidant. Unactivated cyclic and linear internal olefin substrates both reacted in the presence of a catalytic amount of benzoquinone in air to produce skipped dienes. The typical products were structurally confirmed by X‐ray crystallography.     

CH Functionalization of Phenols Using Combined Ruthenium and Photoredox Catalysis: In Situ Generation of the Oxidant

A combination of ruthenium and photoredox catalysis allowed the ortho olefination of phenols. Using visible light, the direct C? H functionalization of o‐(2‐pyridyl)phenols occurred, and diverse phenol ethers were obtained in good yields. The regeneration of the ruthenium catalyst was accomplished by a photoredox‐catalyzed oxidative process.     

Remote meta‐CH Olefination of Phenylacetic Acids Directed by a Versatile U‐Shaped Template

meta‐C? H olefination of phenylacetic acid derivatives has been achieved using a commercially available nitrile‐containing template. The identification of N‐formyl‐protected glycine as the ligand (Formyl‐Gly‐OH) was crucial for the development of this reaction. Versatility of the template approach in accommodating macrocyclopalladation processes with different ring sizes is demonstrated.     

Activation of Strong Boron–Fluorine and Silicon–Fluorine σ‐Bonds: Theoretical Understanding and Prediction

The oxidative addition of BF₃ to a platinum(0) bis(phosphine) complex [Pt(PMe₃)₂] ( 1 ) was investigated by density functional calculations. Both the cis and trans pathways for the oxidative addition of BF₃ to 1 are endergonic (ΔG°=26.8 and 35.7 kcal mol^?1, respectively) and require large Gibbs activation energies (ΔG°^≠=56.3 and 38.9 kcal mol^?1, respectively). A second borane plays crucial roles in accelerating the activation; the trans oxidative addition of BF₃ to 1 in the presence of a second BF₃ molecule occurs with ΔG°^≠ and ΔG° values of 10.1 and ?4.7 kcal mol^?1, respectively. ΔG°^≠ becomes very small and ΔG° becomes negative. A charge transfer (CT), F→BF₃, occurs from the dissociating fluoride to the second non‐coordinated BF₃. This CT interaction stabilizes both the transition state and the product. The B?F σ‐bond cleavage of BF₂Ar^F (Ar^F=3,5‐bis(trifluoromethyl)phenyl) and the B?Cl σ‐bond cleavage of BCl₃ by 1 are accelerated by the participation of the second borane. The calculations predict that trans oxidative addition of SiF₄ to 1 easily occurs in the presence of a second SiF₄ molecule via the formation of a hypervalent Si species.     

Dihydrogen Catalysis of the Reversible Formation and Cleavage of CH and NH Bonds of Aminopyridinate Ligands Bound to (η5‐C5Me5)IrIII

This study focuses on a series of cationic complexes of iridium that contain aminopyridinate (Ap) ligands bound to an (η⁵‐C₅Me₅)Ir^III fragment. The new complexes have the chemical composition [Ir(Ap)(η⁵‐C₅Me₅)]⁺, exist in the form of two isomers ( 1⁺ and 2⁺ ) and were isolated as salts of the BAr_F^? anion (BAr_F=B[3,5‐(CF₃)₂C₆H₃]₄). Four Ap ligands that differ in the nature of their bulky aryl substituents at the amido nitrogen atom and pyridinic ring were employed. In the presence of H₂, the electrophilicity of the Ir^III centre of these complexes allows for a reversible prototropic rearrangement that changes the nature and coordination mode of the aminopyridinate ligand between the well‐known κ²‐N,N′‐bidentate binding in 1⁺ and the unprecedented κ‐N,η³‐pseudo‐allyl‐coordination mode in isomers 2⁺ through activation of a benzylic C?H bond and formal proton transfer to the amido nitrogen atom. Experimental and computational studies evidence that the overall rearrangement, which entails reversible formation and cleavage of H?H, C?H and N?H bonds, is catalysed by dihydrogen under homogeneous conditions.     

Direct Olefination of Fluorinated Benzothiadiazoles: A New Entry to Optoelectronic Materials

Fluorinated olefin‐containing benzothiadiazoles have important applications in optoelectronic materials. Herein, we reported the direct olefination of fluorinated benzothiadiazoles, as catalyzed by palladium. The reaction proceeds under mild reaction conditions and shows high functional‐group compatibility. A preliminary study of the properties of the resulting symmetrical and unsymmetrical olefin‐containing fluorinated benzothiadiazoles in red‐light‐emitting dyes has also been conducted.     

A Stereoselective Aldol Approach for the Total Syntheses of Two 6‐Alkylated 2H‐Pyran‐2‐ones

A simple and highly efficient stereoselective total synthesis of the 6‐alkylated pyranones (6R)‐6‐[(1E,4R,6R)‐4,6‐dihydroxy‐10‐phenyldec‐1‐en‐1‐yl]‐5,6‐dihydro‐2H‐pyran‐2‐one ( 1 ) and (6S)‐5,6‐dihydro‐6‐[(2R)‐2‐hydroxy‐6‐phenylhexyl]‐2H‐pyran‐2‐one ( 2 ) was developed using Crimmins' aldol reaction, SmI₂ reduction, Grubbs‐II‐catalyzed olefin cross‐metathesis, and Still's modified Horner? Wadsworth? Emmons reaction.     

Combining Rhodium and Photoredox Catalysis for CH Functionalizations of Arenes: Oxidative Heck Reactions with Visible Light

Direct, oxidative metal‐catalyzed C? H functionalizations of arenes are important in synthetic organic chemistry. Often, (over‐)stoichoimetric amounts of organic or inorganic oxidants have to be used in these reactions. The combination of rhodium and photoredox catalysis with visible light allows the direct C? H olefination of arenes. Small amounts (1 mol %) of a photoredox catalyst resulted in the efficient C? H functionalization of a broad range of substrates under mild conditions.     

Rhodium(III)‐Catalyzed Selective ortho‐Olefinations of N‐Acyl and N‐Aroyl Sulfoximines by CH Bond Activation

Two new rhodium‐catalyzed oxidative couplings between sulfoximine derivatives and alkenes by regioselective C?H activation, affording ortho‐olefinated (Heck‐type) products, are reported. A synthetic application of the ortho‐alkenylated products into the corresponding cyclic derivatives has been demonstrated, and a mechanistic rational for the rhodium catalysis is presented.     

First Principles (DFT) Characterization of RhI/dppp‐Catalyzed CH Activation by Tandem 1,2‐Addition/1,4‐Rh Shift Reactions of Norbornene to Phenylboronic Acid

The C?H activation in the tandem, “merry‐go‐round”, [(dppp)Rh]‐catalyzed (dppp=1,3‐bis(diphenylphosphino)propane), four‐fold addition of norborene to PhB(OH)₂ has been postulated to occur by a C(alkyl)?H oxidative addition to square‐pyramidal Rh^III?H species, which in turn undergoes a C(aryl)?H reductive elimination. Our DFT calculations confirm the Rh^I/Rh^III mechanism. At the IEFPCM(toluene, 373.15 K)/PBE0/DGDZVP level of theory, the oxidative addition barrier was calculated to be 12.9 kcal mol^?1, and that of reductive elimination was 5.0 kcal mol^?1. The observed selectivity of the reaction correlates well with the relative energy barriers of the cycle steps. The higher barrier (20.9 kcal mol^?1) for norbornyl–Rh protonation ensures that the reaction is steered towards the 1,4‐shift (total barrier of 16.3 kcal mol^?1), acting as an equilibration shuttle. The carborhodation (13.2 kcal mol^?1) proceeds through a lower barrier than the protonation (16.7 kcal mol^?1) of the rearranged aryl–Rh species in the absence of o‐ or m‐substituents, ensuring multiple carborhodations take place. However, for 2,5‐dimethylphenyl, which was used as a model substrate, the barrier for carborhodation is increased to 19.4 kcal mol^?1, explaining the observed termination of the reaction at 1,2,3,4‐tetra(exo‐norborn‐2‐yl)benzene. Finally, calculations with (Z)‐2‐butene gave a carborhodation barrier of 20.2 kcal mol^?1, suggesting that carborhodation of non‐strained, open‐chain substrates would be disfavored relative to protonation.     

Highly Sensitive Electrochemiluminescence Detection of Mercury(II) Ions Based on DNA‐Linked Luminol‐Au NPs Superstructure

A novel highly sensitive electrochemiluminescence (ECL) detection protocol for mercury(II) ions was developed. Based on the strong and stable thymine? thymine mismatches complexes coordination chemistry, mercury(II) ions can specifically bind to a designed DNA strand, leading to the release of the complimentary DNA strand. The released DNA strand was then captured by magnetic beads modified with specific DNA, and then through the formation of DNA‐linked luminol‐Au nanoparticles (NPs) superstructure, a specific ECL system for mercury(II) ions was developed. Using 3‐aminopropyl‐triethoxysilane as an effective enhancer, the ECL system can detect Hg²⁺ ion within a linear range from 2.0×10^?10 mol L^?1 to 2.0×10^?8 M, with a detection limit as low as 1.05×10^?10 M (3σ). Moreover, this ECL system is highly specific for Hg²⁺, without interference from other commonly coexisted metal ions, and it can be used for the analysis of real samples.     

Efficient Access to Substituted Silafluorenes by Nickel‐Catalyzed Reactions of Biphenylenes with Et2SiH2

The reaction of biphenylene ( 1 ) with Et₂SiH₂ in the presence of [Ni(PPhMe₂)₄] results in the formation of a mixture of 2‐diethylhydrosilylbiphenyl [ 2 (Et₂HSi)] and 9,9,‐diethyl‐9‐silafluorene ( 3 ). Silafluorene 3 was isolated in 37.5 % and 2 (Et₂HSi) in 36.9 % yield. The underlying reaction mechanism was elucidated by DFT calculations. 4‐Methyl‐9,9‐diethyl‐9‐silafluorene ( 7 ) was obtained selectively from the [Ni(PPhMe₂)₄]‐catalyzed reaction of Et₂SiH₂ and 1‐methylbiphenylene. By contrast, no selectivity could be found in the Ni‐catalyzed reaction between Et₂SiH₂ and the biphenylene derivative that bears tBu substituents in the 2‐ and 7‐positions. Therefore, two pairs of isomers of tBu‐substituted silafluorenes and of the related diethylhydrosilylbiphenyls were formed in this reaction. However, a subsequent dehydrogenation of the diethylhydrosilylbiphenyls with Wilkinson’s catalyst yielded a mixture of 2,7‐di‐tert‐butyl‐9,9‐diethyl‐9‐silafluorene ( 8 ) and 3,6‐di‐tert‐butyl‐9,9‐diethyl‐9‐silafluorene ( 9 ). Silafluorenes 8 and 9 were separated by column chromatography.     

Reactivity of Oxygen Radical Anions Bound to Scandia Nanoparticles in the Gas Phase: CH Bond Activation

The activation of C?H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O^?.) is an important species in C?H activation. The mechanistic details of C?H activation by O^?. radicals can be well understood by studying the reactions between O^?. containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n‐butane was studied by using a high‐resolution time‐of‐flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n‐butane by (Sc₂O₃)_NO^? (N=1–18) clusters was observed. The reactivity of (Sc₂O₃)_NO^? (N=1–18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc₈O₁₃^?) and 12 (Sc₂₄O₃₇^?). Larger (Sc₂O₃)_NO^? clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc₂O₃)_NO^? (N=1–5) clusters, which were found to contain the O^?. radicals as the active sites. The local charge environment around the O^?. radicals was demonstrated to control the experimentally observed size‐dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O^?. containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C?H bond activation.     

Gelatin Protein‐Mediated Direct Aldol Reaction

Gelatin protein was found to catalyze the aldol reaction between cyclohexanone and different aromatic aldehydes under mild reaction conditions. The aldol additions carried out in DMSO at 37° yielded the addition products with moderate diastereoselectivities favoring the syn isomers. Appropriate control experiments demonstrated the activity of the protein in the aldol reaction. The kinetic study of the model reaction between 4‐nitrobenzaldehyde and cyclohexanone established a first‐order rate constant k=(7.4±0.5)×10^?3 h^?1. Moreover, the scale‐up of the process was successfully achieved at 1‐g scale in a yield comparable to that in small scale.     

Direct Olefination of Alcohols with Sulfones by Using Heterogeneous Platinum Catalysts

Carbon‐supported Pt nanoparticles (Pt/C) were found to be effective heterogeneous catalysts for the direct Julia olefination of alcohols in the presence of sulfones and KOtBu under oxidant‐free conditions. Primary alcohols, including aryl, aliphatic, allyl, and heterocyclic alcohols, underwent olefination with dimethyl sulfone and aryl alkyl sulfones to give terminal and internal olefins, respectively. Secondary alcohols underwent methylenation with dimethyl sulfone. Under 2.5 bar H_2, the same reaction system was effective for the transformation of alcohol OH groups to alkyl groups. Structural and mechanistic studies of the terminal olefination system suggested that Pt⁰ sites on the Pt metal particles are responsible for the rate‐limiting dehydrogenation of alcohols and that KOtBu may deprotonate the sulfone reagent. The Pt/C catalyst was reusable after the olefination, and this method showed a higher turnover number (TON) and a wider substrate scope than previously reported methods, which demonstrates the high catalytic efficiency of the present method.