Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

The oxidative cross‐coupling of aromatic substrates without the necessity of leaving groups or catalysts is described. The selective formation of partially protected nonsymmetric 2,2′‐biphenols via electroorganic synthesis was accomplished with a high yield of isolated product. Since electric current is employed as the terminal oxidant, the reaction is reagent‐free; no reagent waste is generated as only electrons are involved. The reaction is conducted in an undivided cell, and is suitable for scale‐up and inherently safe. The implementation of O‐silyl‐protected phenols in this transformation results in both significantly enhanced yields and higher selectivity for the desired nonsymmetric 2,2′‐biphenols. The use of a bulky silyl group to block one hydroxyl moiety makes the final product less prone to oxidation. Furthermore, the partially silyl‐protected 2,2′‐biphenols are versatile building blocks that usually require tedious or low‐yielding synthetic pathways. Additionally, this strategy facilitates a large variety of new substrate combinations for oxidative cross‐coupling reactions.     

O‐Alkyl S‐3,3‐Dimethyl‐2‐oxobutyl Dithiocarbonates as Versatile Sulfur‐Transfer Agents in Radical C(sp3)?H Functionalization

Boiling of the title compounds in ethereal solvents or cycloalkanes in the presence of a radical initiator leads to radical C(sp³)? H functionalization, by which a sulfur atom is introduced into the ethereal solvents at the oxygenated carbon atom or into the cycloalkanes. Both acyclic and cyclic ethers, such as [18]crown‐6 and [D₈]THF, undergo the sulfur transfer. The reaction is useful for the synthesis of monothioacetals, thiols, and sulfides from simple starting materials.     

Visible‐Light‐Driven Self‐Coupling of Methylarenes Catalyzed by Ni2P@Cd0.5Zn0.5S Nanoparticles

The Ni₂P@Cd_0.5Zn_0.5S nanoparticles photocatalyzed self‐coupling of p‐xylene was reported here, and the corresponding coupling product 1,2‐di‐p‐tolylethane was obtained. The reaction could be extended to toluene derivatives with electron‐donating and electron‐withdrawing substituents. Ni₂P@Cd_0.5Zn_0.5S nanoparticles had already been characterized by XRD, ICP‐AES, SEM, TEM, UV/Vis, FL, XPS. The Mott–Schottky curves of Ni₂P@Cd_0.5Zn_0.5S were made through electrochemical methods. An active carbon free‐radical was captured through ESR measurement under irradiation. The research demonstrated this photocatalytic system feasible for the self‐coupling reaction of toluene derivatives.     

Cu‐Mediated Selective N‐Arylation of Aminotriazole Acyclonucleosides

Novel N‐aryltriazole nucleosides were synthesized via a Cu‐mediated C? N cross‐coupling reaction, using 3‐aminotriazole acyclonucleosides and various boronic acid reagents. Interestingly, N‐arylation proceeded much more rapidly on the amide group than on the amine group, leading to selective N‐arylation of the amide functionality on nucleosides containing both groups on the triazole nucleobase.     

Palladium/Copper‐Cocatalyzed Oxidative Amidobrominations of Alkenes

In the presence of LiBr, a palladium/copper combination catalyzes dehydrogenative amidobrominations of acrylates with NH‐sulfoximines, leading to N‐vinylated products by dual NH/CH coupling, followed by oxidative enamide bromination. Mechanistically, the domino process is proposed to involve palladium(II) species as key intermediates. First synthetic applications of the products have been demonstrated.     

A highly efficient heterogeneous montmorillonite K‐10‐supported palladium catalyst for Suzuki–Miyaura cross‐coupling reaction in aqueous medium

A heterogeneous montmorillonite K‐10‐supported palladium triphenylphosphine catalyst is reported for the Suzuki–Miyaura cross‐coupling reaction at room temperature. A library of electronically diverse aryl bromides and arylboronic acids underwent the cross‐coupling reaction at very good rates in aqueous solvent. The reusability of the catalyst was also examined and it was found to be effective up to three catalytic cycles. Copyright © 2014 John Wiley & Sons, Ltd.     

A Heterogeneous‐Catalyst‐Based,Microwave‐Assisted Protocol for the Synthesis of 2,2′‐Bipyridines

A new method of preparing 2,2′‐bipyridines with short reaction times by using microwave assistance and heterogeneous catalysts has been developed. With a Negishi‐like protocol, it was found that Ni/Al₂O₃–SiO₂ afforded 2,2′‐bipyridine products in up to 86 % yield in 1 h. Palladium supported on alumina also provided yields of 2,2′‐bipyridines comparable to those seen for homogeneous PEPPSI^TM (1,3‐diisopropylimidazol‐2‐ylidene)(3‐chloropyridyl)palladium(II)dichloride) and tetrakis(triphenylphosphanyl)palladium complexes.     

Microwave‐Assisted Palladium‐Catalyzed Direct Arylation of 1,4‐Disubstituted 1,2,3‐Triazoles with Aryl Chlorides

Treatment of 1,4‐disubstituted 1,2,3‐triazoles with aryl chlorides in the presence of potassium carbonate under palladium catalysis and microwave irradiation at 250 °C for 15 min leads to arylation of the triazole at the 5‐position. A variety of functional groups, including ester and hydroxy groups, are compatible. The procedure is suitable for the regioselective preparation of trisubstituted triazoles. Microwave irradiation accelerates the reaction, thus allowing the rapid synthesis of trisubstituted triazoles, which are difficult to synthesize selectively.     

Transition‐metal‐catalyzed Chelation‐assisted C–H Functionalization of Aromatic Substrates

In the past decade, transition‐metal‐catalyzed C–H activations have been very popular in the research field of organometallic chemistry, and have been considered as efficient and convenient strategies to afford complex natural products, functional advanced materials, fluorescent compounds, and pharmaceutical compounds. In this account, we begin with a brief introduction to the development of transition‐metal‐catalyzed C–H activation, especially the development of transition‐metal‐catalyzed chelation‐assisted C–H activation. Then, a more detailed discussion is directed towards our recent studies on the transition‐metal‐catalyzed chelation‐assisted oxidative C–H/C–H functionalization of aromatic substrates bearing directing functional groups.     

Aluminiumhydrazide. Bildung eines dimeren Di(tert‐butyl)aluminiumhydrazids mit viergliedrigem Al2N2‐Heterozyklus und Umsetzung eines Dialkylaluminiumchlorids mit Dilithium‐bis(trimethylsilyl)hydrazid

Aluminium Hydrazides – Formation of a Dimeric Di( tert ‐butyl)aluminium Hydrazide Containing a Four‐Membered Al₂N₂ Heterocycle and Reaction of Dialkylaluminium Chloride with Dilithium Bis(trimethylsilyl)hydrazide The reaction of di(tert‐butyl)aluminium chloride with tert‐butylhydrazine yielded an adduct ( 1 ) which was isolated in a pure form and characterized by crystal structure determination. 1 reacted with n‐butyllithium by deprotonation and salt elimination to give the corresponding di(tert‐butyl)aluminium hydrazide ( 2 ), which is a dimer in solution and in the solid state and possesses a four‐membered Al₂N₂ heterocycle with two exocyclic N–N bonds. The structure of 2 differs from that of other di(tert‐butyl)aluminium hydrazides which have four‐ or five‐membered heterocycles. Treatment of impure samples of 1 with n‐butyllithium yielded by the cleavage of the N–N bonds a mixture of several unknown products, from which the dimeric, centrosymmetric aluminium amide [(Me₃C)₂AlN(H)CMe₃]₂ ( 3 ) was isolated. A similar product ( 4 ) was obtained in a low yield by the reaction of (Me₃SiCH₂)₂AlCl with the dilithium hydrazide Li₂N₂(SiMe₃)₂. An intact N–N bond was neither found in the second product isolated from this reaction. Instead a tricyclic compound was formed by C–H activation which has two five‐membered AlNSiC₂ heterocycles bridged by Al–N bonds.     

Photochemical Reactions of Regioisomeric 2,2‐Dimethyl‐5,5‐diphenyl‐ and 5,5‐Dimethyl‐2,2‐diphenyl‐Substituted Diazo Ketones of a Tetrahydrofuran Series

The principal direction of conventional photolysis of the regioisomeric 2,2‐dimethyl‐5,5‐diphenyl‐ and 5,5‐dimethyl‐2,2‐diphenyl‐substituted 4‐diazodihydrofuran‐3(2H)‐ones 1a and 1b , respectively, is the Wolff rearrangement, while other photochemical processes, which are giving rise to the formation of C? H‐insertion, 1,2‐alkyl‐ or ‐aryl‐shifts, as well as H‐atom‐abstraction products occur to a much lower degree (Schemes 2 and 3). The ratio of similar reaction products from both regioisomers 1a and 1b is essentially independent of their structure, and a substantial effect of the relative position of the Ph and diazo group to each other on the yield of C? H‐insertion products does not occur. Based on stereochemical considerations, the Wolff rearrangement of diazodihydrofuran‐3(2H)‐ones apparently proceeds in a concerted manner, whereas the appearance in the reaction mixture of 1,2‐shift and H‐atom‐abstraction products points to the parallel generation during photolysis of singlet and triplet carbenes (Schemes 4 and 5).     

Asymmetric Desymmetrization via Metal‐Free C−F Bond Activation: Synthesis of 3,5‐Diaryl‐5‐fluoromethyloxazolidin‐2‐ones with Quaternary Carbon Centers

We disclose the first asymmetric activation of a non‐activated aliphatic C?F bond in which a conceptually new desymmetrization of 1,3‐difluorides by silicon‐induced selective C?F bond scission is a key step. The combination of a cinchona alkaloid based chiral ammonium bifluoride catalyst and N,O‐bis(trimethylsilyl)acetoamide (BSA) as the silicon reagent enabled the efficient catalytic cycle of asymmetric C_sp3?F bond cleavage under mild conditions with high enantioselectivities. The ortho effect of the aryl group at the prostereogenic center is remarkable. This concept was applied for the asymmetric synthesis of promising agrochemical compounds, 3,5‐diaryl‐5‐fluoromethyloxazolidin‐2‐ones bearing a quaternary carbon center.     

Organo‐Palladium(II)‐Verbindungen mit PdC4‐Koordination: Phenylethinyl‐ und Methylphenylethinylkomplexe

Tetrakis(p‐tolyl)oxalamidinato‐bis[acetylacetonatopalladium(II)] ([Pd₂(acac)₂(oxam)]) reacted with Li–C≡C–C₆H₅ in THF with formation of [Pd(C≡C–C₆H₅)₄Li₂(thf)₄] ( 1a ). Reaction of [Pd₂(acac)₂(oxam)] with a mixture of 6 equiv. Li–C≡C–C₆H₅ and 2 equiv. LiCH₃ resulted in the formation of [Pd(CH₃)(C≡C–C₆H₅)₃Li₂(thf)₄] ( 2 ), and the dimeric complex [Pd₂(CH₃)₄(C≡C–C₆H₅)₄Li₄(thf)₆] ( 3 ) was isolated upon reaction of [Pd₂(acac)₂(oxam)] with a mixture of 4 equiv. Li–C≡C–C₆H₅ and 4 equiv. LiCH₃. 1 – 3 are extremely reactive compounds, which were isolated as white needles in good yields (60–90%). They were fully characterized by IR, ¹H‐, ¹³C‐, ⁷Li‐NMR spectroscopy, and by X‐ray crystallography of single crystals. In these compounds Li ions are bonded to the two carbon atoms of the alkinyl ligand. 1a reacted with Pd(PPh₃)₄ in the presence of oxygen to form the already known complexes trans‐[Pd(C≡C–C₆H₅)₂(PPh₃)₂] and [Pd(η²‐O₂)(PPh₃)₂]. In addition, 1a is an active catalyst for the Heck coupling reaction, but less active in the catalytic Sonogashira reaction.     

Sonogashira coupling using PdEnCat™: a copper‐, phosphine‐, amine‐ and microwave‐free alternative to the preparation of arylalkynes

Sonogashira coupling of iodo‐ and bromoarenes and acetylenes using PdEnCat™ 30 in a phosphine‐, copper‐, amine‐, and microwave‐free system was developed, which allows for the preparation of a modulator of glutamate receptor mGluR5. Copyright © 2011 John Wiley & Sons, Ltd.     

Oxygenase‐Catalyzed Desymmetrization of N,N‐Dialkyl‐piperidine‐4‐carboxylic Acids

γ‐Butyrobetaine hydroxylase (BBOX) is a 2‐oxoglutarate dependent oxygenase that catalyzes the final hydroxylation step in the biosynthesis of carnitine. BBOX was shown to catalyze the oxidative desymmetrization of achiral N,N‐dialkyl piperidine‐4‐carboxylates to give products with two or three stereogenic centers.     

Amidophosphine‐stabilized palladium complexes catalyse Suzuki–Miyaura cross‐couplings in aqueous media

We report a simple and efficient procedure for Suzuki–Miyaura reactions in aqueous media catalysed by amidophosphine‐stabilized palladium complexes trans‐{L³PPh₂}₂PdCl₂ ( 3 ), trans‐{L³PPhtBu}₂PdCl₂ ( 4 ), [Pd(η³‐C₃H₅)(L³PPh₂)Cl] ( 5 ) and {Pd[2‐(Me₂NCH₂)C₆H₄](L³PPh₂)Cl} ( 6 ). The acidity of the NH proton in complexes 3 , 4 , 5 , 6 plays an important role in their catalytic activity. In addition, the palladium complexes cis‐{L¹PPh₂}PdCl₂ ( 1 ) and trans‐{L²PPh₂}₂PdCl₂ ( 2 ) stabilized by phosphines containing Y,C,Y‐chelating ligands L^1,2 have also been found to be useful catalysts for Suzuki–Miyaura reactions in aqueous media. The method can be effectively applied to both activated and deactivated aryl bromides yielding high or moderate conversions. The catalytic activity of couplings performed in pure water increases when utilizing a Pd complex with more acidic NH protons. A decrease of palladium concentration from 1.0 to 0.5 mol% does not lead to a substantial loss of conversion. In addition, Pd complex 1 can be efficiently recovered using two‐phase system extraction. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of four series of quinoline‐based heterocycles by reacting 2‐chloroquinoline‐3‐carbonitriles with various types of isocyanides

Four distinct sets of functionalized quinolines were synthesized by reacting 2‐chloroquinoline‐3‐carbonitriles with various types of isocyanides under appropriate conditions. The palladium‐catalysed reaction of less hindered aliphatic and aromatic isocyanides with 2‐chloroquinoline‐3‐carbonitriles yielded 2‐alkyl(aryl)‐1‐imino‐1H‐pyrrolo[3,4‐b]quinolin‐3(2H)‐one derivatives; however, the catalysed reaction of more hindered isocyanides such as tert‐butyl isocyanide produced the corresponding 3‐cyanoquinoline‐2‐carboxamides. Interestingly, chloroquinoline‐3‐carbonitriles reacted with ethyl isocyanoacetate in the presence of Cs₂CO₃ to generate imidazo[1,5‐a]quinoline derivatives; notably, tosylmethyl isocyanide under the same conditions formed unprecedented 2‐tosyl‐3‐cyanoquinolines.