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.     

Synthesis of Aryl Carbamates via Copper‐Catalyzed Coupling of Aryl Halides with Potassium Cyanate

Coupling of aryl halides with potassium cyanate takes place at 100–110 °C in alcohols under the catalysis of CuI (cuprous iodide) and 2‐(2,6‐dimethylphenylamino)‐2‐oxoacetic acid, affording the corresponding aryl carbamates with great diversity.     

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.

     

Palladium‐Catalyzed Decarboxylative sp‐sp2 Cross‐Coupling Reactions of Aryl and Vinyl Halides and Triflates with α,β‐Ynoic Acids using Silver Oxide

Palladium‐catalyzed decarboxylative sp‐sp² cross‐coupling reactions of aryl and vinyl halides and triflates with α,β‐ynoic acids using silver oxide have been developed. A variety of α,β‐ynoic acids were readily decarboxylated in the presence of silver oxide and then, generated in situ, silver acetylides were coupled with electrophiles in the presence of a palladium(0) catalyst under neutral conditions, producing either symmetrical or unsymmetrical diarylacetylenes, arylalkylacetylenes and arylvinylacetylenes in good to excellent yields.     

Ligand‐Free Copper‐Catalyzed Amination of Heteroaryl Halides with Alkyl‐ and Arylamines

N‐Heteroarylations of alkyl‐ and arylamines with various heteroaryl halides have been achieved by ligand‐free copper‐catalyzed cross‐couplings affording aminopyridines and aminopyrimidines in moderate to high yields (up to 99% yield).     

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.     

A Metal‐Free Approach Toward Saturated N‐Propargyl Heterocycles via an Annulation/Decarboxylative Coupling Sequence

A three‐component reaction of a 1,2‐amino alcohol or 1,3‐amino alcohol with a formaldehyde solution and a propiolic acid was developed and studied. This new strategy provided an efficient access to biologically and synthetically important N‐propargyl oxazolidines, 1,3‐oxazinanes and thiazolidine bearing a diverse range of substituents in good yields. The transformation involves a cascade process that begins with an annulation and is followed by the metal‐free decarboxylative coupling.

     

An Amine‐, Copper‐ and Phosphine‐Free Sonogashira Coupling Reaction Catalyzed by Immobilization of Palladium in Organic–Inorganic Hybrid Materials

An immobilization of palladium in organic‐inorganic hybrid materials‐catalyzed Sonogashira coupling reaction has been described. Terminal alkynes reacted with aryl iodides and aryl bromides only in the presence of a 3‐(2‐aminoethylamino)propyl‐functionalized, silica gel‐immobilized palladium catalyst under amine‐, copper‐ and phosphine‐free reaction conditions. The reaction generates the corresponding cross‐coupling products in excellent yields. Furthermore, the silica‐supported palladium can be recovered and recycled by a simple filtration of the reaction solution and used for 30 consecutive trials without any decreases in activity.     

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).     

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.     

An Improved Protocol for Palladium‐Catalyzed Alkoxycarbonylations of Aryl Chlorides with Alkyl Formates

The palladium‐catalyzed alkoxycarbonylation of aryl and heteroaryl halides using butyl formate has been investigated. In the presence of palladium(II) acetate/n‐butylbis(1‐adamantyl)phosphine ( L1 ), and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as base for the first time non‐activated chloroarenes can be conveniently carbonylated in good yields.     

Ligand‐Free Reusable Palladium‐Catalyzed Heck‐Type Coupling Reactions of Hypervalent Iodine Reagents under Mild Conditions

Highly effective palladium‐catalyzed Heck‐type couplings of hypervalent iodine reagents are reported for the first time. It is noteworthy that such reactions could be carried out in the absence of ligand at 40 °C and the catalytic system could be easily reused for five times.     

Synthesis of 3,4‐Disubstituted Quinolin‐2‐(1H)‐ones via Palladium‐Catalyzed Decarboxylative Arylation Reactions

The Pd‐catalyzed decarboxylative cross‐coupling reaction of 4‐substituted quinolin‐2(1H)‐one‐3‐carboxylic acids with (hetero)aryl halides is described. With palladium(II) bromide and triphenylarsine ligand as the catalyst system, a variety of 4‐substituted 3‐(hetero)aryl quinolin‐2(1 H)‐ones and related heterocycles, such as 4‐substituted 3‐arylcoumarins can be prepared in good to excellent yields.     

A General and Practical Palladium‐Catalyzed Direct α‐Arylation of Amides with Aryl Halides

An efficient system for the direct catalytic intermolecular α‐arylation of acetamide derivatives with aryl bromides and chlorides is presented. The palladium catalyst is supported by Kwong’s indole‐based phosphine ligand and provides monoarylated amides in up to 95% yield. Excellent chemoselectivities (>10:1) in the mono‐ and diarylation with aryl bromides were achieved by careful selection of bases, solvents, and stoichiometry. Under the coupling conditions, the weakly acidic α‐protons of amides (pK_a up to 35) were reversibly depotonated by lithium tert‐butoxide (LiO‐t‐Bu), sodium tert‐butoxide (NaO‐t‐Bu) or sodium bis(trimethylsilyl)amide [NaN(SiMe₃)₂].

     

Synthesis of N‐Arylamides by Copper‐Catalyzed Amination of Aryl Halides with Nitriles

A copper‐catalyzed amination of aryl halides with nitriles has been developed. The use of nitriles as nitrogen nucleophiles can make the synthesis of N‐arylamides more simple than that using amides through in‐situ hydrolysis. A variety of N‐arylamides and benzoxazole derivatives can be synthesized according to this approach.     

Decarboxylative Coupling of α‐Keto Acids with ortho‐Phenylenediamines Promoted by an Electrochemical Method in Aqueous Media

An electrochemical method for the decarboxylative coupling of α‐keto acids with ortho‐phenylenediamines was developed. The reaction proceeded smoothly in aqueous solution under air and metal catalyst‐free conditions to afford 2‐substituted benzimidazoles in good yields. Benzothiazoles could also be synthesized by this protocol.

     

钯催化草酸钾盐与碘苯脱羧偶联反应的研究

利用乙二酸单乙酯酸钾和碘苯在钯催化条件下脱羧偶联反应.通过改变催化剂、溶剂得到了最优化的反应条件:以三氟乙酸钯为催化剂,N-甲基吡咯烷酮为溶剂,乙二酸单乙酯酸钾和碘苯于140℃得到产率为82％的苯甲酸乙酯;同样乙二酸单丁酯酸钾也取得了理想的收率.     

Efficient Heterogeneously Palladium‐Catalysed Heck Arylation of Acrolein Diethyl Acetal. Selective Synthesis of Cinnamaldehydes or 3‐Arylpropionic Esters

A heterogeneous tetrakis(ammine)palladium‐NaY zeolite {[Pd(NH₃)₄]/NaY} catalyst was applied successfully to the Heck arylation of acrolein diethyl acetal using a large variety of aryl and heteroaryl bromides. Depending on the reaction conditions (Heck versus Cacchi) good to high selectivities toward the 3‐arylpropionic esters or to the cinnamaldehydes were achieved, respectively. Under classical Heck conditions, while the catalyst was found to be stable over the two first runs, it showed significant loss of activity from the third cycle. Under Cacchi conditions, the catalyst could not be reused as it led to high dehalogenation rates. All results indicate that the reactions proceed through dissolved palladium species in the bulk solution (leaching). As observed by transmission electronic microscopic (TEM) analyses, while these species can be trapped and stabilised by the zeolite framework under the Heck conditions, they tend to form large palladium(0) aggregates under the Cacchi conditions leading to dehalogenation rather than to the expected Heck coupling.     

Synthesis of Dienes by Palladium‐Catalyzed Couplings of Tosylhydrazones with Aryl and Alkenyl Halides

Two different combinations of coupling partners can be employed for the synthesis of conjugated dienes by palladium‐catalyzed cross‐coupling with tosylhydrazones: α,β‐unsaturated ketone and aryl halide or alkenyl halide and non‐conjugated tosylhydrazone. Depending on the substrate, a vinylogous hydride elimination is responsible for the formation of the final dienes.