Platinum on Carbon‐Catalyzed Hydrodefluorination of Fluoroarenes using Isopropyl Alcohol‐Water‐Sodium Carbonate Combination

We have developed a platinum on carbon‐isopropyl alcohol‐catalyzed and widely applicable defluorination method for fluoroarenes, and the addition of water and sodium carbonate efficiently accelerated the reaction. The defluorination readily occurred under the reaction conditions in comparison with the dehalogenation of other aromatic halides (fluorine>chlorine>bromine≫iodine).     

Palladium on Carbon‐Catalyzed Cross‐Coupling using Triarylbismuths

Simple and efficient protocols for the 10% palladium on carbon (Pd/C)‐catalyzed cross‐coupling reactions between triarylbismuths and aryl halides have been developed. A variety of iodo‐ and bromobenzenes possessing an electron‐withdrawing group on the aromatic nucleus were smoothly cross‐coupled in the presence of 10% Pd/C, sodium phosphate dodecahydrate (Na₃PO₄⋅12 H₂O) and 1,4‐diazabicyclo[2.2.2]octane (DABCO) in heated N‐methyl‐2‐pyrrolidone (NMP) as the solvent. For the arylations of iodobenzenes, the reactions effectively proceeded under the combined use of caesium fluoride (CsF) and 2,2′‐biquinoline. Furthermore, a ligand‐free 10% Pd/C‐catalyzed cross‐coupling reaction between the aryl iodides and triarylbismuths was also established by the addition of tetra‐n‐buthylammonium fluoride trihydrate (TBAF⋅3 H₂O) in which the palladium metals were hardly leached from the catalyst into the reaction media.     

Recent Advances in Transition Metal‐Catalyzed Hydrogenation of Nitriles

Amines are important building blocks possessing various applications in agrochemicals, the fine chemical industry, pharmaceuticals, materials science and biotechnology. The catalytic hydrogenation of nitriles is an important reaction for the one‐step synthesis of diverse amines. However, significant amounts of side product formation during the course of the reaction is a major issue. In recent years, an enormous amount of work has been reported using both homogeneous and heterogeneous transition metal complex catalysts for the selective reduction of nitriles. Transition metal catalysts are the most crucial factor that controls the selectivity in this reaction. Therefore, transition metal catalysts are the central point of this review. We have also briefly discussed the effect of reaction parameters, selectivity to different substrate structures and reaction mechanisms. This review provides an overview of recent developments in transition metal‐catalyzed nitrile reduction along with examples which highlight its vast potential in organic transformations.

     

Palladium on Carbon‐Catalyzed One‐Pot N‐Arylindole Synthesis: Intramolecular Aromatic Amination,Aromatization, and Intermolecular Aromatic Amination

Indole and indoline derivatives were selectively and temperature dependently synthesized via the intramolecular cross‐coupling reaction between the amino and aromatic bromine functionalities of 2‐bromophenethylamine derivatives in the presence of 10% palladium on carbon (Pd/C), 1,1′‐bis(diphenylphosphino)ferrocene (DPPF), and sodium tert‐butoxide (NaO‐t‐Bu) in mesitylene at 140 and 200 °C, respectively. The neutralization using acetic acid after formation of the indoline derivatives effectively promoted their aromatization, and the corresponding indole derivatives were obtained at 140 °C. Furthermore, various aryl groups were also introduced to the N‐1 position of the indole, pyrrole, and carbazole rings by their direct intramolecular arylation with aryl halides and a one‐pot protocol for N‐arylindole synthesis from 2‐bromophenethylamine was developed.

     

Platinum on Carbon‐Catalyzed H–D Exchange Reaction of Aromatic Nuclei due to Isopropyl Alcohol‐Mediated Self‐ Activation of Platinum Metal in Deuterium Oxide

An efficient and simple deuteration method of arenes using the platinum on carbon‐isopropyl alcohol‐cyclohexane‐deuterium oxide combination under hydrogen gas‐free conditions was accomplished. Since the hydrogen–deuterium exchange reaction cannot be promoted without isopropyl alcohol, zerovalent platinum metal (on carbon) is self‐activated by the in situ‐generated very low amount of hydrogen or hydrogen–deuterium gas derived from isopropyl alcohol or isopropyl alcohol‐d₁. Deuterium‐labeled compounds with high deuterium contents can be easily isolated by the filtration of platinum on carbon and simple extraction. The present hydrogen gas‐free method is safe from the viewpoint of process chemistry and various arenes possessing a variety of reducible functionalities within the molecule could be effectively and directly deuterium‐labeled without undesired reduction.     

Palladium on Carbon‐Catalyzed Synthesis of Benzil Derivatives from 1,2‐Diarylalkynes with DMSO and Molecular Oxygen as Dual Oxidants

A palladium on carbon (Pd/C)‐catalyzed synthetic method for the preparation of benzil derivatives from 1,2‐diarylalkynes has been established using dimethyl sulfoxide (DMSO) and molecular oxygen as dual oxidants. Regardless of the electrical nature of the functional groups on the aromatic rings, 1,2‐diarylalkynes were oxidized to the corresponding benzil derivatives in high to excellent yields. Furthermore, the oxidation could efficiently be catalyzed by both the dry and wet types of Pd/C under atmospheric conditions.     

Chemoselective Ruthenium‐Catalyzed Reduction of Acid Chlorides to Aldehydes with Dimethylphenylsilane

A variety of aromatic and alkyl acid chlorides can be selectively converted into aldehydes using dimethylphenyl silane (HSiMe₂Ph) as the reducing reagent in the presence of the cationic ruthenium catalyst {Cp[(i‐Pr)₃P]Ru(NCMe)₂}⁺ [PF₆]⁻. The reactions proceed under very mild conditions and are tolerant to many functional groups.     

Copper‐in‐Charcoal‐Catalyzed,Tandem One‐Pot Diazo Transfer‐Click Reactions

Copper‐in‐charcoal (Cu/C) is an effective heterogeneous catalyst for tandem diazo transfer/click reactions. In the presence of Cu/C, various azides can be generated in situ from the corresponding amines, and subsequently undergo [3+2] cycloaddition with terminal alkynes to afford triazoles in good yields. The catalyst is also easily recycled.     

Palladium on Carbon‐Catalyzed C−H Amination for Synthesis of Carbazoles and its Mechanistic Study

10% Palladium on carbon (10% Pd/C) successfully catalyzed the intramolecular C−H amination of various N‐mesylated 2‐aminobiphenyls in the presence of a catalytic amount of pyridine N‐oxide in heated dimethyl sulfoxide (DMSO) under an oxygen atmosphere to afford the corresponding N‐mesylcarbazoles. The reaction would proceed via a single‐electron transfer process based on its significant suppression by the addition of a single‐electron scavenger, tetracyanoquinodimethane (TCNQ), and the substituents on the aromatic rings of the substrate have an insignificant effect on the reaction progress.

     

Chemo‐Catalyzed Pathways to Lactic Acid and Lactates

Lactic acid is an important building block for the production of biodegradable polymers (PLLA, PDLA, etc.) as well as starting material for the pharmaceutical industry. The current production of this chiral compound is dominated by fermentation processes. However many catalytic reactions that could be used for manufacturing lactic acid were developed in the past three decades. High reaction rates and simple separation of products in comparison to fermentation characterize many of these processes. Excellent stereoselectivities up to 99% ee could be achieved. This review aims to give a critical overview of chemical processes applying catalysis as an alternative for the production of both enantiomerically pure and racemic lactic acid and lactates. The efficiency and economy of these processes are analyzed.

     

Enantioselective Platinum‐Catalyzed Silicon‐Boron Addition to 1,3‐Cyclohexadiene

Silaboration of 1,3‐cyclohexadiene in the presence of Pt(acac)₂, DIBALH, and a phosphoramidite prepared from (S)‐1,1′‐bi‐2‐naphthol and diisopropylamine led to (1R,4S)‐1‐(dimethylphenylsilyl)‐4‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐2‐cyclohexene with 70% ee. Chiral catalysts based on Ni gave no or essentially racemic product, whereas complexes containing Pd were inactive.     

Lipase/Acetamide‐Catalyzed Carbon‐Carbon Bond Formations: A Mechanistic View

A lipase B from Candida antarctica (CALB)/acetamide‐catalyzed Michael addition of less‐activated ketones and aromatic nitroolefins has been developed, which is particularly interesting because neither CALB nor acetamide can independently catalyze the reaction to any appreciable extent. This co‐catalyst system was applicable to the Michael additions of cyclic and acyclic ketones to a series of aromatic and heteroaromatic nitroolefins. Hydrogen bonds between acetamide and cyclohexanone were confirmed for the observed activation by experimental facts, and new mechanistic insights into CALB/acetamide co‐catalysis are presented.     

Facile Preparation of 2‐Substituted Benzoxazoles and Benzothiazoles via Aerobic Oxidation of Phenolic and Thiophenolic Imines Catalyzed by Polymer‐Incarcerated Platinum Nanoclusters

Platinum nanoclusters supported on a polymer/carbon black composite material was found to be an excellent catalyst for the oxidative cyclization of phenolic and thiophenolic Schiff bases to 2‐substituted benzoxazoles and benzothiazoles under ambient conditions.     

Ligand‐Free and Heterogeneous Palladium on Carbon‐Catalyzed Hetero‐Suzuki–Miyaura Cross‐Coupling

A ligand‐free and heterogeneous palladium on carbon (Pd/C)‐catalyzed hetero‐Suzuki–Miyaura coupling reaction has been developed. The protocol enables the construction of both heterocyclic‐alicyclic and heterocyclic‐heterocyclic biaryl derivatives in good to excellent yields. Furthermore, Pd/C could be reused. The time‐course study clarified that palladium was leached into the reaction media as the reaction proceeded and then completely deposited on the carbon support.     

Substitution‐ and Elimination‐Free Phosphorylation of Functionalized Alcohols Catalyzed by Oxidomolybdenum Tetrachloride

Among 14 oxidometallic species examined for catalytic phosphorylation of the tested alcohols, oxidomolybdenum tetrachloride (MoOCl₄) was found to be the most efficient with a negligible background reaction mediated by triethylamine (Et₃N). The new catalytic protocol can be applied to the chemoselective phosphorylations of primary, secondary and tertiary alcohols as well as the substitution‐free phosphorylations of allylic, propargylic, and benzylic alcohols. Functionalized alcohols bearing acetonide, tetrahydropyranyl ether, tert‐butyldimethylsilyl ether, or ester group are also amenable to the new catalytic protocol. The most difficult scenarios involve substitution‐free phosphorylations of 1‐phenylethanol and 1‐(2‐naphthyl)ethanol which can be effected in 95 and 90% yields, respectively. ESI‐MS, IR, ¹H, and ³¹P NMR spectroscopic analyses of the reaction progress suggest the intermediacy of an alkoxyoxidomolybdenum trichloride‐triethylamine adduct such as [(RO)Mo(O)Cl₃‐Et₃N] to be responsible for the catalytic turnover.     

Catalytic Carbon‐Fluorine Bond Activation with Monocoordinated Nickel‐Carbene Complexes: Reduction of Fluoroarenes

Monocoordinate nickel/N‐heterocyclic carbene complexes reveal unexpected reactivity towards aryl fluorides. Defluorination reactions were efficiently performed with a β‐hydrogen‐containing alkoxide (3 equiv.) in the presence of 3 mol % of [1:1] Ni(0)/IMes⋅HCl catalyst (IMes=1,3‐dimesitylimidazol‐2‐ylidene).     

Candida antarctica Lipase B (CAL‐B)‐Catalyzed Carbon‐Sulfur Bond Addition and Controllable Selectivity in Organic Media

A novel enzymatic, promiscuous protocol for Candida antarctica lipase B (CAL‐B)‐catalyzed carbon‐sulfur bond addition is described. Some control experiments have been designed to demonstrate the catalytic specificity of CAL‐B. Selectivity between anti‐Markovnikov addition and Markovnikov addition was achieved in different organic media. A series of thioether‐containing ester functional groups was synthesized under the catalysis of CAL‐B at 50 °C. All the products were characterized by spectroscopic methods (IR, NMR, ESI‐MS).     

Platinum Nanoparticles Supported on Ionic Liquid‐Modified Magnetic Nanoparticles: Selective Hydrogenation Catalysts

A method for supporting platinum nanoparticles on magnetite nanoparticles is described. The method requires modification of the surface of the magnetic nanoparticles with ionic liquid groups. Before modification, the magnetic nanoparticles are not stable and easily aggregate and, after modification, the magnetite nanoparticles become highly stable and soluble in polar or non‐polar organic solvents depending on the alkyl group of the linked ionic liquids. The supporting of platinum nanoparticles on the modified magnetic nanoparticles was achieved by adsorbing platinum salts (K₂PtCl₄) on the surface of the magnetite nanoparticles via ion exchange with the linked ionic liquid groups and then reducing them by hydrazine. The supported platinum nanoparticles were applied in the catalytic hydrogenation of alkynes in which cis‐alkenes were selectively produced, and in the hydrogenation of α,β‐unsaturated aldehydes where the allyl alcohols were obtained as the exclusive products. The new catalyst can be easily separated from the reaction mixtures by applying an external magnetic field and recycled.     

The Synthesis of Important Pharmaceutical Building Blocks by Palladium‐Catalyzed Coupling Reaction: Access to Various Arylhydrazines

Various arylhydrazones have been successfully synthesized via a highly efficient palladium‐catalyzed cross‐coupling reaction between aryl halides and benzophenone hydrazone. All the reaction parameters have been studied and coupling products were obtained with excellent yields from the corresponding bromides or chlorides.     

Copper(I)‐Catalyzed [3+2] Cycloaddition/Ring‐Opening Rearrangement/[4+2] Cycloaddition/Aromatization Cascade: An Unprecedented Chemo‐ and Stereoselective Three Component Coupling of Sulfonyl Azide,Alkyne and N‐Arylidenepyridin‐2‐ amine to Pyrido[1,2‐a]pyrimidin‐4‐imine

A novel synthetic protocol for the one‐pot chemo‐ and stereoselective construction of diversely functionalized pyrido[1,2‐a]pyrimidin‐4‐imines via copper(I)‐catalyzed [3+2] cycloaddition/ring‐opening rearrangement/[4+2] cycloaddition/aromatization cascade of sulfonyl azides, alkynes and N‐arylidenepyridin‐2‐amines under mild reaction conditions is reported. In addition, the catalytic activity of copper(I)‐modified zeolite, a recyclable, heterogeneous catalyst is also investigated, which gives improved yield compared to its homogeneous equivalents.