Ligand effects in palladium‐catalyzed Suzuki and Heck coupling reactions

A range of sterically hindered diimine ligands and their palladium (II) complexes were synthesized. These compounds were fully characterized by elemental analysis, ¹H and ¹³C‐NMR spectroscopy. The use of the palladium complexes as catalysts for Suzuki and Heck coupling has been studied in an attempt to demonstrate the effect of side groups on catalytic activity. It was clearly seen that the location of side ? CH₃ groups which bound to benzene ring had little effect on catalytic activity. Interestingly when we changed these ? CH₃ groups with ? Cl groups the activity of the complexes increased. On the other hand, side groups which bound to imine nitrogen also had a large effect on catalytic activity. Copyright © 2008 John Wiley & Sons, Ltd.     

Hiyama cross‐coupling reaction catalyzed by a palladium salt of 1‐benzyl‐4‐aza‐1‐azoniabicyclo[2.2.2]octane chloride under microwave irradiation

An efficient catalytic system using 1‐benzyl‐4‐aza‐1‐azoniabicyclo[2.2.2]octane chloride ((BeDABCO)₂Pd₂Cl₆) was developed for the Hiyama cross‐coupling reaction of various aryl halides with triethoxy(phenyl)silane. The substituted biaryls were produced in excellent yields in short reaction times using a catalytic amount of this catalyst in NMP at 100 °C. Copyright © 2014 John Wiley & Sons, Ltd.     

Novel pyridine‐bis(ferrocene‐isoxazole) ligand: synthesis and application to palladium‐catalyzed Sonogashira cross‐coupling reactions under copper‐ and phosphine‐free conditions

We present here the first synthesis and application to Sonogashira reaction of pyridine‐bis(ferrocene‐isoxazole) Pd(II) complex 5 , prepared from 2,6‐bis‐(5‐ferrocenylisoxazole‐3‐yl)pyridine. Under copper‐ and phosphine‐free conditions, the stable complex 5 efficiently catalyzed the cross‐coupling of aryl halides with terminal alkynes in DMF–H₂O with TBAB as an additive, hexahydropyridine as base and affording internal arylated alkynes in moderate to excellent yields. Copyright © 2008 John Wiley & Sons, Ltd.     

Pd‐catalyzed ligand‐free desulfitative Heck reaction with arenesulfinic acid salts under air

Palladium‐catalyzed cross‐coupling reactions of various aryl sulfinic acid salts with a wide variety of vinyl substrates have been achieved in good to excellent yields under simple aerobic conditions at 70°C with the assistance of Cu(II) salts. The reaction can be accelerated by the combination of DMSO with THF. The reported Matsuda–Heck type coupling reactions are tolerant to the common functional groups, making these transformations as attractive alternatives to the traditional cross‐coupling approaches. Copyright © 2013 John Wiley & Sons, Ltd.     

Ligand‐ and solvent‐free synthesis of 2‐aminobenzothiazoles by copper‐catalyzed tandem reaction of 2‐haloanilines with isothiocyanates

We report an environmentally friendly, efficient and practical method for the synthesis of 2‐aminobenzothiazoles by a copper(II)‐catalyzed tandem reaction of 2‐haloanilines with isothiocyanates under ligand‐ and solvent‐free conditions in air. The developed methodology conforms to the principles of 'green chemistry' and addresses the shortage of such methods for the synthesis of 2‐aminobenzothiazoles. The reaction is quite general and generates a variety of 2‐aminobenzothiazoles in good to excellent yields. Copyright © 2012 John Wiley & Sons, Ltd.     

Single‐Flask Multicomponent Palladium‐Catalyzed α,γ‐Coupling of Ketone Enolates: Facile Preparation of Complex Carbon Scaffolds

A three‐component palladium‐catalyzed reaction sequence has been developed in which γ‐substituted α,β‐unsaturated products are obtained in a single flask by an α‐alkenylation with either a subsequent γ‐alkenylation or γ‐arylation of a ketone enolate. Coupling of a variety of electronically and structurally different components was achieved in the presence of a Pd/Q‐Phos catalyst (2 mol %), usually at 22 °C with yields of up to 85 %. Most importantly, access to these products is obtained in one simple operation in place of employing multiple reactions.     

Ligand‐Controlled α‐ and β‐Arylation of Acyclic N‐Boc Amines

The palladium‐catalyzed ligand‐controlled arylation of α‐zincated acyclic amines, obtained by directed α‐lithiation and transmetalation, is described. Whereas PtBu₃ gave rise to α‐arylated Boc‐protected amines, more flexible N‐phenylazole‐based phosphine ligands induced major β‐arylation through migrative cross‐coupling.     

Palladium‐Catalyzed Oxidative Difunctionalization of Alkenes with α‐Carbonyl Alkyl Bromides Initiated through a Heck‐type Insertion: A Route to Indolin‐2‐ones

The oxidative interception of various σ‐alkyl palladium(II) intermediates with additional reagents for the difunctionalization of alkenes is an important research area. A new palladium‐catalyzed oxidative difunctionalization reaction of alkenes with α‐carbonyl alkyl bromides is described, in which the σ‐alkyl palladium(II) intermediate is generated through a Heck insertion and trapped using an aryl C(sp²)? H bond. This method can be applied to various α‐carbonyl alkyl bromides, including primary, secondary, and tertiary α‐bromoalkyl esters, ketones, and amides.     

Ligand‐free Pd/Cu‐catalyzed decarboxylative coupling of aryl iodides with α‐oxocarboxylates

This paper describes a palladium/copper‐catalyzed decarboxylative coupling of aryl iodides with α‐oxocarboxylates. The cross‐coupling reaction gives high chemical yields of aryl ketones and has wide functional group tolerance, making the transformation an attractive alternative to the traditional cross‐coupling approaches for aryl ketones. Copyright © 2014 John Wiley & Sons, Ltd.     

Protecting‐group‐free palladium‐catalyzed hydroxylation,C–O and C–N coupling of chiral 6‐bromo‐ and 6,6’‐dibromo‐ 1,1’‐binaphthols

A straightforward, protecting‐group‐free protocol for the synthesis of chiral 6‐substituted and 6,6’‐disubstituted binols (binol = 1,1’‐bi‐2‐naphthol) by palladium‐catalyzed hydroxylation, C–N and C–O coupling of chiral 6‐bromo‐ and 6,6’ ‐dibromo‐1,1’‐binaphthols is developed. The protecting group free palladium‐catalyzed hydroxylation, C–O and C–N cross‐coupling protocol affords a straightforward and general method for the synthesis of chiral 6‐substituted and 6,6’‐disubstituted binols with good yields, avoiding the tedious procedures of introduction and removal of protecting groups. Copyright © 2013 John Wiley & Sons, Ltd.     

Immobilized Pd on (S)‐methyl histidinate‐modified multi‐walled carbon nanotubes: a powerful and recyclable catalyst for Mizoroki–Heck and Suzuki–Miyaura C–C cross‐coupling reactions in green solvents and under mild conditions

A stable and powerful heterogeneous palladium catalyst was synthesized using immobilized palladium on (S)‐methyl histidinate bonded onto the surface of multi‐walled carbon nanotubes. The catalyst was characterized using a combination of Fourier transform infrared and X‐ray photoelectron spectroscopies, transmission electron microscopy, X‐ray powder diffraction and inductively coupled plasma, thermogravimetric and elemental analyses. This new air‐ and moisture‐stable phosphine‐free palladium catalyst was found to be highly active and reusable in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions in poly(ethylene glycol) and aqueous ethanol as green solvents using an extremely small amount of palladium under mild conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

Tetraphosphine/palladium‐catalyzed Suzuki–Miyaura coupling of heteroaryl halides with 3‐pyridine‐ and 3‐thiopheneboronic acid: an efficient catalyst for the formation of biheteroaryls

An easily prepared tetraphosphine N,N,N′,N′‐tetra(diphenylphosphinomethyl)‐1,2‐ethylenediamine (L1) associated with [Pd(η³‐C₃H₅)Cl]₂ affords an efficient catalyst for Suzuki–Miyaura coupling of 3‐pyridineboronic acid with heteroaryl bromides. Reaction could be performed with as little as 0.02 mol% catalyst and a high turnover number of 2500 is obtained. A wide range of substrates is investigated with satisfactory yields, and good compatibility with aminogroup‐substituted pyridines and unprotected indole is exhibited. This protocol can also be applied successfully to the reaction of heteroaryl bromides with 3‐thiopheneboronic acid. This Pd‐tetraphosphine catalyst efficiently restrains the poisoning effect from heteroaryls, and shows good stability and longevity. Copyright © 2013 John Wiley & Sons, Ltd.     

Palladium‐catalyzed synthesis of 6‐allylcoumarins using organotin reagents as multicoupling organometallic nucleophiles

Derivatives of 6‐iodocoumarin undergoing a direct Stille cross‐coupling reaction with organotin compounds in the presence of a catalytic amount of Pd(PPh₃)₄ in dimethylformamide at 80°C is described in this study. It is the first report of the palladium‐catalyzed coupling of iodocoumarins with allyltributyltin under mild conditions to form alkylcoumarin compounds in good yields. © 2014 The Authors. Applied Organometallic Chemistry published by John Wiley & Sons, Ltd.     

Polystyrene‐supported Pd(II)–N‐heterocyclic carbene complex as a heterogeneous and recyclable precatalyst for cross‐coupling of acyl chlorides with arylboronic acids

Palladium‐catalysed cross‐coupling reaction of aroyl chlorides with arylboronic acids was achieved in the presence of polystyrene‐supported palladium(II)–N‐heterocyclic carbene complex, using K₂CO₃ in acetone–water, providing diaryl ketones in high yields. Furthermore, the heterogeneous catalyst could be reused up to four times without significant loss of activity.     

Kryptofix 5 as an inexpensive and efficient ligand for the palladium‐catalyzed Mizoroki‐Heck reaction

A novel complex of PdCl₂ with a multidentate cryptand ligand, Kryptofix 5, has been prepared and characterized by various techniques including ¹H‐ and ¹³C NMR spectroscopy, Fourier transform infrared (FT‐IR), Raman, ultraviolet and visible (UV‐VIS) spectroscopy, inductively coupled plasma (ICP), CHN elemental and energy dispersive X‐ray analysis (EDX). This heat‐ and air‐stable complex was utilized as a highly active catalyst for the Mizoroki‐Heck reaction of aryl halides with various olefins. Interestingly, it was found that aryl bromides as well as aryl iodides were efficiently cross‐coupled with terminal alkenes at 130 °C in 10 min. Furthermore, the least reactive aryl chlorides reacted with styrene to obtain the desired products in acceptable yields.     

Palladium‐catalyzed synthesis of 8‐allyl or 8‐prenylcoumarins by using organotin reagents as multicoupling nucleophiles

In this study, 8‐iodocoumarin derivatives underwent a direct Stille cross‐coupling reaction with several organotin compounds in the presence of a catalytic amount of Pd(PPh₃)₄ in DMF at 80 °C. The cross‐coupling reaction proceeded smoothly under mild conditions and permitted the formation of 8‐allyl or 8‐prenylcoumarin compounds in good yields. Copyright © 2012 John Wiley & Sons, Ltd.     

Four‐Component Borocarbonylation of Vinylarenes Enabled by Cooperative Cu/Pd Catalysis: Access to β‐Boryl Ketones and β‐Boryl Vinyl Esters

We report here a general four‐component synthetic procedure for the preparation of β‐boryl ketones and β‐boryl vinyl esters. Joint catalyzed by palladium and copper catalysts, borocarbonylative reaction between vinylarenes, aryl halides/triflates, B₂Pin₂, and carbon monoxide proceed successfully. A variety of synthetically useful β‐boryl ketones were synthesized in good to high yields by using aryl iodides as the substrates. It is noteworthy that when aryl triflates were applied as the starting materials, β‐boryl vinyl esters were synthesized in a similar manner and with broad functional group tolerance. A rational mechanism for this reaction was also proposed.     

Application of Pd‐2A3HP‐MCM‐41 to the Suzuki,Heck and Stille coupling reactions and synthesis of 5‐substituted 1H‐tetrazoles

An ecofriendly heterogeneous catalyst has been synthesized by anchoring palladium onto the surface of organically modified mesoporous silica. The prepared catalyst was characterized using X‐ray diffraction, Fourier transform infrared and energy‐dispersive X‐ray spectroscopies, transmission and scanning electron microscopies, inductively coupled plasma and thermogravimetric techniques. The catalyst shows high activity in the Suzuki, Heck and Stille cross‐coupling reactions and the synthesis of 5‐substituted 1H‐tetrazoles from sodium azide (NaN₃). These methods have the advantages of high yields, green reaction conditions, simple methodology and easy separation and workup. Copyright © 2016 John Wiley & Sons, Ltd.     

Stereoselective Synthesis of 1,3-Enynylstannanes via Palladium Catalyzed Cross-Coupling Reactions of （Z）-α-Bromovinylstannanes

Based on the different reactivity of stannyl and bromo groups, (Z)-α-bromovinylstannanes can undergo the cross-coupling reaction with alkynyl Grignard reagents in the presence of tetrakis(triphenylphosphine)palladium(0) catalyst in THF at room temperature to afford stereoselectively 1,3-enynylstannanes in good yields.