Visible‐Light Photoredox‐Catalyzed and Copper‐Promoted Trifluoromethoxylation of Arenediazonium Tetrafluoroborates

We report the development of photoredox‐catalyzed and copper‐promoted trifluoromethoxylation of arenediazonium tetrafluoroborates, with trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxylation reagent. This new method takes advantage of visible‐light photoredox catalysis to generate the aryl radical under mild conditions, combined with copper‐promoted selective trifluoromethoxylation. The reaction is scalable, tolerates a wide range of functional groups, and proceeds regioselectively under mild reaction conditions. Furthermore, mechanistic studies suggested that a Cs[Cu(OCF₃)₂] intermediate might be generated during the reaction.     

Additive‐Free Gold(III)‐Catalyzed Stereoselective Synthesis of 2‐Deoxyglycosides Using Phenylpropiolate Glycosides as Donors

Stereoselective synthesis of deoxyglycosides has been achieved from benchtop stable and easily synthesizable deoxy‐phenylpropiolate glycosides (D‐PPGs) using gold(III) salt as catalyst under external additive‐free conditions. Under a simple catalytic system, D‐PPGs reacted with a variety of sugar and non‐sugar acceptors to produce majorly α‐stereoselective O/N‐deoxyglycosides in good to excellent yields and regenerate easily separable and reusable phenylpropiolic acid. Deoxy‐PPGs containing armed and disarmed groups survived well under the optimized reaction conditions. In addition, the orthogonal nature of D‐PPGs was showcased, and 1,1′‐linked trehalose‐type sugar was also synthesized.     

Synthesis and reactivity of some imidazo‐, triazolo‐ and tetrazolo‐isoquinoline derivatives

1‐Acetylirrüno‐3‐methyl‐1H‐isochromene‐4‐carbonitrile, 1 , reacts with glycine ethyl ester under basic conditions to give an imidazo[2,1‐a]isoquinoline derivative, while reaction with hydrazine hydrate in 1,4‐dioxane, with further chemistry, provides access to [1,2,4]triazolo[5,1‐a]isoquinoline, [1,2,4]triazolo[3,4‐a]isoquinoline and tetrazolo[5,1‐a]isoquinoline analogs. Benzene ring nitration and radical bromination of substituent methyl groups were investigated in the four tricycles, with some different positional reactivities being found. Two bromomethyl derivatives so produced were oxidised; ethyl 2‐bromomethyl‐6‐cyano‐5‐methylimidazo[2,1‐a]isoquinoline‐3‐carboxylate gave the anticipated ethyl 6‐cyano‐2‐formyl‐5‐methylimidazo[2,1‐a]isoquinoline‐3‐carboxylate (which reacted further with hydrazine to form a new system, 8,9‐dihydro‐6‐methyl‐8‐oxopyridazino[4′,5′:4,5]imidazo[2,1‐a]isoquinoline‐5‐carbonitrile), while 5‐bromomethyl‐2‐methyl[1,2,4]triazolo[5,1‐a]isoquinoline‐6‐carbonitrile unexpectedly gave directly another new system, 5,6‐dihydro‐5‐hydroxy‐2‐methyl‐7H‐pyrrolo[3,4‐c][1,2,4]triazolo[5,1‐a]isoquinolin‐7‐one.     

CaII‐Catalyzed Alkenylation of Alcohols with Vinylboronic Acids

Direct alkenylation of a variety of alcohols with vinylboronic acids has been accomplished using the air‐stable calcium(II) complex Ca(NTf₂)₂ under mild conditions with short reaction times. For reluctant transformations, an ammonium salt was used as an additive to circumvent the reactivity issue.     

Copper‐Promoted Annulation of Terminal Alkynes with 2‐Aminopyridines to Assemble 2‐Halogenated Imidazo[1,2‐a]pyridines

Copper‐promoted annulation reactions of terminal alkynes with 2‐aminopyridines have been developed for the synthesis of 2‐halogenated imidazo[1,2‐a]pyridines using copper halide as the halogen source. A variety of substrates survived under the reaction conditions and gave the desired products in good yields. This reaction features advantages such as easily available starting materials, broad substrate scope, and mild reaction conditions.     

Copper‐Mediated Formation of Aryl,Heteroaryl, Vinyl and Alkynyl Difluoromethylphosphonates: A General Approach to Fluorinated Phosphate Mimics

A general and efficient access to aryl, heteroaryl, vinyl and alkynyl difluoromethylphosphonates is described. The developed methodology using TMSCF₂PO(OEt)₂, iodonium salts and a copper salt provided a straightforward manifold to reach these highly relevant products. The reaction proved to be highly functional group tolerant and proceeded under mild conditions, giving the corresponding products in good to excellent yields. This method represents the first general synthetic route to this important class of fluorinated scaffolds, which are well‐recognized as in vivo stable phosphate surrogates.     

Syntheses,Structures, and Catalytic Activities of Copper(I) Complexes with the Ligand 2(4,5‐Diphenyl‐1H‐imidazol‐2‐yl)­pyridine

Two copper(I) complexes of compositions [Cu(HL)I]₂ · EtOH ( 1 ) and [Cu(HL)₃]I · MeOH ( 2 ) were synthesized via the reactions of HL [HL = 2(4,5‐diphenyl‐1H‐imidazol‐2‐yl)pyridine] and CuI in EtOH and MeOH, respectively, under solvothermal conditions. The complexes were characterized by X‐ray single crystal diffraction, IR spectroscopy, and elemental analysis. Compounds 1 and 2 are catalytically active towards ketalization reaction, giving various ketals under mild conditions.     

Copper‐Mediated Formation of Aryl,Heteroaryl, Vinyl and Alkynyl Difluoromethylphosphonates: A General Approach to Fluorinated Phosphate Mimics

A general and efficient access to aryl, heteroaryl, vinyl and alkynyl difluoromethylphosphonates is described. The developed methodology using TMSCF₂PO(OEt)₂, iodonium salts and a copper salt provided a straightforward manifold to reach these highly relevant products. The reaction proved to be highly functional group tolerant and proceeded under mild conditions, giving the corresponding products in good to excellent yields. This method represents the first general synthetic route to this important class of fluorinated scaffolds, which are well‐recognized as in vivo stable phosphate surrogates.     

Pd‐catalyzed Desulfitative reaction of Aryltrifluoroborates with sodium Arenesulfinates in water

An efficient procedure for the synthesis of biaryls was catalyzed by Pd(CH₃CN)₄(BF₄)₂ is reported. This Pd‐catalyzed cross‐coupling reaction of aryltrifluoroborates with sodium arenesulfinates was developed under mild and environmentally benign conditions, in water without any ligand or additive. The reaction gave a range of structurally diverse unsymmetrical bi‐aryl molecules with excellent yields, in which the byproduct was sulfur dioxide. It is worth noting that this protocol is also applicable to many heterocyclic aromatics such as thiophene, furan, pyridine, quinoline, isoquinoline and indole.     

(BeDABCO)2Pd2Cl6 as an efficient homogeneous catalyst for copper‐free Sonogashira cross‐coupling reaction

An efficient catalytic system using 1‐benzyl‐4‐aza‐1‐azoniabicyclo[2.2.2]octane chloride and palladium chloride ((BeDABCO)₂Pd₂Cl₆) was developed for the Sonogashira reaction. In the presence of a catalytic amount of this efficient, stable homogeneous catalytic system that is non‐sensitive to air and moisture, various aryl halides were efficiently coupled with phenylacetylene in good yields in H₂O at 50°C under copper‐free conditions. Benzyl dabco as an efficient ligand and also a quaternary ammonium salt had an efficient stabilizing effect on the Pd(0) species. Copyright © 2014 John Wiley & Sons, Ltd.     

Practical Iron‐ and Cobalt‐Catalyzed Cross‐Coupling Reactions between N‐Heterocyclic Halides and Aryl or Heteroaryl Magnesium Reagents

The reaction scope of iron‐ and cobalt‐catalyzed cross‐coupling reactions in the presence of isoquinoline (quinoline) in the solvent mixture tBuOMe/THF has been further investigated. Various 2‐halogenated pyridine, pyrimidine, and triazine derivatives were arylated under these mild conditions in excellent yields. The presence of isoquinoline allows us to perform Fe‐catalyzed cross‐coupling reactions between 6‐chloroquinoline and aryl magnesium reagents. Furthermore, it was found that the use of 10 % N,N‐dimethylquinoline‐8‐amine increases the yields of some Co‐catalyzed cross‐coupling reactions with chloropyridines bearing electron‐withdrawing substituents.     

Nickel‐Catalyzed Cyclization of ortho‐Iodoketoximes and ortho‐Iodoketimines with Alkynes: Synthesis of Highly Substituted Isoquinolines and Isoquinolinium Salts

A convenient method for the synthesis of highly substituted isoquinolines and isoquinolinium salts by the nickel‐catalyzed cyclization of ortho‐haloketoximes and ‐ketimines, respectively, with alkynes is described. The reaction of ortho‐haloketoximes and various alkynes in the presence of [Ni(PPh₃)₂Br₂] and zinc powder in a mixture of acetonitrile and tetrahydrofuran at 80 °C for 15 hours gave 1,3,4‐trisubstituted isoquinoline products in moderate to excellent yields and high regioselectivity. The corresponding isoquinoline N‐oxide was found to be the intermediate in the cyclization reaction pathway. In contrast, the reaction of ortho‐haloketimines and alkynes under similar catalytic conditions in tetrahydrofuran at 70 °C for two hours gave 1,2,3,4‐tetrasubstituted isoquinolinium salts in good to excellent yields.     

Dehydrative Glycosylation Enabled by a Comproportionation Reaction of 2‐Aryl‐1,3‐dithiane 1‐Oxide†

Summaryof main observation and conclusion A new dehydrativeglycosylation reaction has been established by capitalizing on the compropor-tionation reaction of 2-aryl-1,3-dithiane 1-oxides promoted by triflic anhydride(Tf2O).By wedding the high potency of thiophilic promoter system with the step efficiency of dehydrative glycosylation,this reagentunderwent facile intermolecular oxothio acetalization with C1-hemiacetal donor to install a temporary leaving group,rendering a transient electrophilic center at the remote site to the anomeric position.The sulfenyltriflate tethered at the ter-minus concomitantly activated the sulfide intramolecularly to afford the oxocarbenium ion,thereby facilitating the title glycosylation.Aside from accom-modating broad range functional groups and inactive hemiacetal substrates,the present activation protocol also proved expedient for 1,3-diol protection.Most importantly,this method further provided a fresh perspective for the application of sulfur chemistry to carbohydrate chemistry.     

Copper‐Catalyzed Electrophilic Etherification of Arylboronic Esters with Isoxazolidines

A copper‐catalyzed electrophilic etherification of arylboronic esters is reported. Isoxazolidines are utilized as easily available and stable [RO]⁺ surrogates to give 1,3‐amino aryl ethers. The O‐selective arylation of isoxazolidines takes place without causing competitive N‐arylation. In contrast to previously reported anionic conditions, our copper‐catalyzed conditions are mild enough to achieve high functional group tolerance. Preliminary mechanistic studies and DFT calculations support that the reaction proceeds via a transmetalation/oxidative addition pathway, followed by a Lewis acid‐promoted reductive elimination to induce the crucial O‐selectivity.     

Stable but Reactive Perfluoroalkylzinc Reagents: Application in Ligand‐Free Copper‐Catalyzed Perfluoroalkylation of Aryl Iodides

The aromatic perfluoroalkylation catalyzed by a copper(I) salt with bis(perfluoroalkyl)zinc reagents Zn(R_F)₂(DMPU)₂, which were prepared and then isolated as a stable white powder from perfluoroalkyl iodide and diethylzinc, was accomplished to provide the perfluoroalkylated products in good‐to‐excellent yields. The advantages of this reliable and practical catalytic reaction are 1) air‐stable and easy‐to‐handle bis(perfluoroalkyl)zinc reagents can be utilized, 2) the reagent is reactive and hence the operation without activators and ligands is simple, and 3) not only trifluoromethylation but also perfluoroalkylation can be attained.     

Metal‐Free Intramolecular Carbocyanation of Alkenes: Catalytic Stereoselective Construction of Pyrrolo[2,1‐a]isoquinolines with Multiple Substituents

The first catalytic stereoselective approach to prepare multiple substituted cyclic nitriles by means of a novel metal‐free intramolecular carbocyanation strategy has been developed, which provided an efficient protocol to construct densely functionalized diastereoenriched pyrrolo[2,1‐a]isoquinoline derivates under mild reaction conditions (up to 20/1 d.r., 98 % yield).     

Visible‐Light‐Promoted Dearomative Fluoroalkylation of β‐Naphthols through Intermolecular Charge Transfer

The first visible‐light‐promoted dearomative fluoroalkylation of β‐naphthols was realized without the assistance of any transition‐metal catalysts or external photosensitizers. Inexpensive fluoroalkyl iodides were directly used as efficient fluoroalkylation reagents under very mild reaction conditions. The scope of this process was found to be general and broad, and both trifluoromethyl and perfluoroalkyl groups (‐C₄F₉, ‐C₆F₁₃, and ‐C₈F₁₇) were installed in excellent yields. Preliminary mechanistic studies suggest that visible‐light‐promoted intermolecular charge transfer within the naphtholate–fluoroalkyl iodide electron donor–acceptor (EDA) complex induces a single electron transfer in the absence of photocatalysts.     

Copper‐Catalyzed Intermolecular Trifluoromethylazidation of Alkenes: Convenient Access to CF3‐Containing Alkyl Azides

A novel copper‐catalyzed intermolecular trifluoromethylazidation of alkenes has been developed under mild reaction conditions. A variety of CF₃‐containing organoazides were directly synthesized from a wide range of olefins, including activated and unactivated alkenes, and the resulting products can be easily transformed into the corresponding CF₃‐containing amine derivatives.     

Palladium‐Catalysed C(sp3)−H Glycosylation for the Synthesis of C‐Alkyl Glycoamino Acids

We have developed a highly efficient and practical approach for palladium‐catalyzed trifluoroacetate‐promoted N‐quinolylcarboxamide‐directed glycosylation of inert β‐C(sp³)?H bonds of N‐phthaloyl α‐amino acids with glycals under mild conditions. For the first time, C(sp³)?H activation for glycosylation was achieved to build C‐alkyl glycosides. This method facilitates the synthesis of various β‐substituted C‐alkyl glycoamino acids and offers a tool for glycopeptide synthesis.     

A novel hydrophobic copper complex supported on γ‐Fe2O3 as a magnetically heterogeneous catalyst for one‐pot three‐component synthesis of α‐aminophosphonates

A novel hydrophobic copper complex supported on γ‐Fe₂O₃ is synthesized and characterized by different methods such as FT‐IR, XRD, TEM, SEM, TGA, VSM, ICP and CHN analysis. It was used as a magnetically recyclable heterogeneous catalyst for the efficient synthesis of α‐aminophosphonates via a one‐pot three‐component reaction under solvent‐free conditions. The present catalytic system worked extremely well for the synthesis of α‐aminophosphonates even up to five subsequent trails without significant loss of its catalytic activity or copper leaching. The TEM image and FT‐IR spectrum of the catalyst after five times recovery showed that the structure of the catalyst was stable under the reaction conditions with no change being observed. The strong magnetic properties of the reused catalyst were revealed by complete and easy attraction using an external magnet and also by VSM curve. This work represents the first and unique example of a hydrophobic copper complex for catalysis in water generating reactions.