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.     

A Practical Procedure for Iron‐Catalyzed Cross‐Coupling Reactions of Sterically Hindered Aryl‐Grignard Reagents with Primary Alkyl Halides

Although iron‐catalyzed cross‐coupling reactions of arylmagnesium halides with alkyl halides are well established and proceed effectively under a variety of experimental conditions, they often find limitations when working with sterically hindered aryl‐Grignard reagents. Outlined in this paper is a practical solution that allows this gap in coverage to be filled. Specifically, it is shown that bis(diethylphosphino)ethane (depe) crafts an effective coordination environment about Fe(+2). This commercially available ligand is slim enough not to interfere with the loading of the iron center even by ortho,ortho‐disubstituted arylmagnesium halides, yet capable of preventing premature reductive coupling of the resulting organoiron species, which seem to be hardly basic either. The reaction is compatible with various polar functional groups as well as with substrates containing β‐heteroatom substituents. Moreover, the procedure even allows encumbered neopentylic electrophiles to be arylated with donors as bulky as mesitylmagnesium bromide, whereas secondary alkyl halides tend to eliminate.

     

Chemoselective Synthesis of Unsymmetrical Internal Alkynes or Vinyl Sulfones via Palladium‐Catalyzed Cross‐Coupling Reaction of Sodium Sulfinates with Alkynes

A highly efficient and mild palladium‐catalyzed cross‐coupling of sodium sulfinates and alkynes for the selective synthesis of unsymmetrical internal alkynes and vinyl sulfones has been developed. This methodology has advantages of easily accessible starting materials, functional group tolerance and a wide range of substrates, which provides rapid access to alkynes and vinyl sulfones.

     

Iron‐Catalysed sp3–sp3 Cross‐Coupling Reactions of Unactivated Alkyl Halides with Alkyl Grignard Reagents

Iron‐catalysed sp³–sp³ Kumada coupling with primary and secondary alkyl halides (RX) and alkyl Grignard reagents has been achieved in low to good yields depending on the nature of the R group.     

Synthesis of Benzoxazole and Benzimidazole Derivatives via Ligand‐Free Copper(I)‐Catalyzed Cross‐Coupling Reaction of o‐Halophenols or o‐Haloanilines with Carbodiimides

A novel and efficient synthesis of benzoxazole and benzimidazole derivatives via a ligand‐free, copper(I)‐catalyzed, one‐pot cascade process has been developed. A variety of carbodiimides coupled with o‐halophenols or o‐haloanilines to give the products in moderate to excellent yields under the mild conditions.     

Iron‐Catalyzed Mizoroki–Heck Cross‐Coupling Reaction with Styrenes

In the presence of iron(II) chloride (FeCl₂; 20 mol%) and potassium tert‐butoxide (t‐BuOK; 4 equiv.) in dimethyl sulfoxide (DMSO), aryl and heteroaryl iodides undergo stereoselective Mizoroki–Heck C C cross‐coupling reactions with styrenes at 60 °C giving the corresponding (E)‐alkenes. The best yields are obtained upon adding a ligand (80 mol%) such as proline or picolinic acid. Aryl bromides and pyridinyl bromides are also coupled with styrenes but in lower yields.     

Nickel(0)/Imidazolium Carbene Catalyst System for Efficient Cross‐Coupling of Aryl Bromides and Chlorides with Organomanganese Reagents

N,N′‐Bis(2,6‐diisopropylphenyl)imidazolium chloride associated with nickel(II) acetylacetonate (3–5 mol %) was used as catalyst to efficiently cross‐couple functionalized aryl bromides with organomanganese reagents. The reactions were performed between 0 °C and room temperature, giving unsymmetrical biaryls in 0.25 to 24 h with 52 to 100 % yields for isolated materials. Aryl chlorides showed slightly diminished reactivity in Ni/2 IPr‐catalyzed cross‐couplings and good yields could only be attained with activated or neutral substrates.     

Samarium Powder‐Catalyzed Palladium‐Free and Ligand‐Free Sonogashira Coupling Reactions

A study of samarium powder‐catalyzed cross‐coupling reactions of aryl halides with terminal alkynes is described. The couplings performed in the polyethylene glycol PEG‐600 provided the corresponding coupling products in good yields. The first example of palladium‐free, copper‐free and amine‐free catalytic system for Sonogashira couplings is presented in the absence of ligand.     

Practical Iron‐Catalyzed Allylations of Aryl Grignard Reagents

An operationally simple iron‐catalyzed reductive cross‐coupling reaction between aryl halides and allyl electrophiles has been developed. The underlying domino process exhibits high versatility with respect to the allylic leaving group (acetate, tosylate, diethyl phosphate, methyl carbonate, trimethylsilanolate, methanethiolate, chloride, bromide) and high economic and environmental sustainability with respect to the catalyst system (0.2–5 mol% tris(acetylacetonato)iron(III), ligand‐free) and reaction conditions (tetrahydrofuran, 0 °C, 45 min).     

Palladium‐Catalyzed Cross‐Coupling Reaction Using Arylgermanium Sesquioxide

Powdery reagents obtained by complete alkaline hydrolysis of arylgermanium trichlorides were found to undergo the palladium‐catalyzed cross‐coupling reaction with aryl bromides and iodides in good yields. The reaction is performed in an aqueous medium taking sodium hydroxide as an activator. Some base‐sensitive functionalities such as acetyl and trifluoromethyl groups survived the reaction.     

Ligand‐Free Iron/Copper Cocatalyzed Alkynylation Coupling Reactions

Ligand‐free iron/copper cocatalyzed cross‐coupling reactions of aryl halides with terminal alkynes were carried out to provide the corresponding coupling products in good yields (up to 99%). Noteworthy is that this low‐cost, effective and environmentally friendly protocol was the first to be employed in alkynylation couplings.     

Cobalt‐Catalyzed Reductive Cross‐Coupling Between Benzyl Chlorides and Aryl Halides

A new protocol for the direct reductive cobalt‐catalyzed arylation of benzyl chlorides has been developed in order to form functionalized diarylmethanes. A variety of reactive groups either on the aryl or the benzyl halide was employed. This represents the first cobalt‐catalyzed reductive cross‐coupling which does not require any ligand and pyridine. A reaction pathway is proposed involving a radical benzyl species.

     

User‐Friendly Methylation of Aryl and Vinyl Halides and Pseudohalides with DABAL‐Me3

An extremely technically simple cross‐methylation of aryl and vinyl halides and pseudohalides using an air‐stable adduct of trimethylaluminium with a Pd(0) catalyst supported by commercially available biarylphosphines gives excellent yields of methylated products (mainly >95%). Reactions can be run with either 0.5 mol % catalyst or without requiring the exclusion of atmospheric oxygen or the drying of solvents in some cases. A wide variety of functional groups is tolerated including CN, OH, CO₂R, CHO and NO₂.     

Handy Protocols using Vinyl Nosylates in Suzuki–Miyaura Cross‐Coupling Reactions

Vinyl nosylates derived from 1,3‐dicarbonyl compounds could be engaged in Suzuki–Myaura cross coupling reactions with aryl‐, vinyl‐ and methylboronic acids or trifluoborate derivatives at room temperature in the presence of 2 mol% of [1,1′‐bis(diphenylphosphino)ferrocene]dichloropalladium(II) [PdCl₂(dppf)]. One‐pot procedures have been set up for practical and efficient nosylation–cross‐coupling reactions. Nosylate, as a cheap novel pseudo‐halide, gives very stable compounds and is very efficient in Suzuki–Myaura cross coupling reactions (21 examples, 44–99%).

     

Ligandless Copper‐Catalyzed Coupling of Heteroaryl Bromides with Gaseous Ammonia

A range of different N‐ and S‐containing heterocyclic bromides can be efficiently coupled with gaseous ammonia in the presence of copper(II) acetylacetonate [Cu(acac)₂] as catalyst and in the absence of additional ligands. Unstable aminothiophenes and aminobenzothiophenes can be further reacted in situ to afford functionalized derivatives.     

Palladium‐Catalyzed Desulfitative Cross‐Coupling Reaction of Sodium Arylsulfinates with H‐Phosphonate Diesters

A novel and convenient palladium‐catalyzed cross‐coupling reaction of H‐phosphonate diesters with sodium arylsulfinates was developed via desulfitation in the presence of silver carbonate and tetra‐butylammonium chloride. This method is highly efficient and provides a rapid access to a broad spectrum of arylphosphonate diesters in good to excellent yields.

     

Alkylboronic Esters from Palladium‐ and Nickel‐Catalyzed Borylation of Primary and Secondary Alkyl Bromides

Palladium‐ and nickel‐catalyzed cross‐coupling recations of unactivated alkyl bromides with diboron reagents have been developed as practical methods for the synthesis of primary and secondary alkylboronic esters. These reactions extend the concept and utility of Pd‐ and Ni‐catalyzed cross‐coupling of aliphatic electrophiles. They also show different substrate selectivity and ligand dependence as compared to the recently reported Cu‐catalyzed borylation reaction.     

Rhodium‐Catalyzed Cross‐Coupling of Alkenyl Halides with Arylboron Compounds

The rhodium(I)‐catalyzed reaction between arylboronic esters and excess 1,2‐dichloroethene selectively afforded (2‐chlorovinyl)arenes. Double arylation yielding 1,2‐diarylethenes was observed when 1,2‐dibromoethene was reacted with 2.5 equivalents of arylboronic acid.