Palladium on Carbon: An Efficient,Heterogeneous and Reusable Catalytic System for Carbonylative Synthesis of N‐Substituted Phthalimides

The application of palladium on carbon (Pd/C) as a heterogeneous recyclable catalyst was investigated for the double carbonylation of o‐dihaloarenes with amines providing excellent yield of N‐substituted phthalimides in shorter reaction time as compared to earlier reported homogeneous protocols. Furthermore, the scope of the developed protocol was applied for the synthesis N‐substituted phthalimides from o‐halobenzoates and o‐halobenzoic acid via a single step carbonylative cyclization reaction. The developed methodology describes an efficient one‐step approach for the synthesis of an important class of heterocycles and tolerates a wide variety of functional groups. It circumvents the use of phosphine ligands with an additional advantage of catalyst recyclability for up to eight consecutive cycles.     

Palladium‐Catalyzed One‐Pot Synthesis of 5‐(1‐Arylvinyl)‐1H‐benzimidazoles: Overcoming the Limitation of Acetamide Partners

A new one‐pot palladium‐catalyzed process between N‐tosylhydrazones, N‐(dihalophenyl)‐imidates, and amines was designed. This reaction involves Barluenga cross‐coupling and N‐arylation followed by cyclization to produce functionalized benzimidazoles. During this transformation, one C C bond and two C N bonds were created by a single palladium‐catalyzed reaction. Depending on the starting materials, a library of 5‐(1‐arylvinyl)‐1H‐benzimidazoles was synthesized. Among several arylvinylbenzimidazole derivatives evaluated, one compound exhibits excellent antiproliferative activity in the nanomolar concentration range against human colon carcinoma cell lines (HCT‐116) and human lung adenocarcinoma epithelial cell lines (A549).

     

Palladium‐Catalyzed Synthesis of Selectively Substituted Phenanthridine Derivatives

Selectively substituted phenanthridine derivatives are obtained by a facile reaction of o‐alkylated aryl iodides, o‐bromoarenesulfonylanilines and activated olefins in the presence of palladium and norbornene as catalysts. The reaction takes place under mild conditions to give the products in satisfactory yields using readily available starting materials.     

Using aluminium triflate as a co‐catalyst for the polymerization of o‐phenylenediamine and its derivatives

Aromatic diamine monomers, including o‐phenylenediamine (oPD), 4‐methyl‐o‐phenylenediamine (4Me‐oPD), 4,5‐dimethyl‐o‐phenylenediamine (dMe‐oPD) and 4‐(tert‐butyl)‐o‐phenylenediamine (tBu‐oPD), were polymerized by chemical oxidation using ammonium persulfate as an oxidant. Aluminium triflate (Al(OTf)₃) was also used for the first time as a co‐catalyst under various reaction conditions for the polymerization of oPD derivatives. The polymerization yield was improved when Al(OTf)₃ was introduced to the polymerization reaction for most polymers. The solubility of poly(4‐methyl‐o‐phenylenediamine) (P(4Me‐oPD)), poly(4,5‐dimethyl‐o‐phenylenediamine) (P(dMe‐oPD)) and poly(4‐(tert‐butyl)‐o‐phenylenediamine) (P(tBu‐oPD)) polymers was improved compared with the poly(o‐phenylenediamine) (P(oPD)) polymers in most common solvents. The homopolymers obtained were characterized by Fourier transform IR spectroscopy, UV?visible spectroscopy, ¹H and ¹³C NMR, wide‐angle X‐ray diffraction, DSC and TGA. The results showed that the yield, solubility and structure of the polymers are significantly dependent on the polymerization conditions. DSC measurements indicated that the polymers exhibited melting and crystallization transitions. The polymers also showed good thermal stability and decompose above 400 °C in nitrogen. © 2013 Society of Chemical Industry     

Synthesis of Benzimidazole‐Substituted Arylboronic Acids via Aerobic Oxidation of 1,2‐Arylenediamines and Formyl‐Substituted Aryl MIDA Boronates using Potassium Iodide as a Catalyst

A highly efficient protocol for the synthesis of benzimidazole‐substituted arylboronic acids was developed via aerobic oxidative cyclization of 1,2‐aryldiamines and formyl‐substituted aryl MIDA (N‐methyliminodiacetic acid) boronates using potassium iodide as a nucleophilic catalyst. Furthermore, a one‐pot protocol for the synthesis of benzimidazole‐substituted arylboronic acids from 1,2‐phenylenediamines and formyl‐substituted arylboronic acids was developed without the isolation of any intermediates. The resulting boronic acids were further subjected to Suzuki–Miyaura coupling reactions without isolation, leading to diaryl‐substituted benzimidazoles with only one separation step.

     

Synthesis of 1H‐Indole‐3‐carboxamidines through a Palladium‐Catalyzed Three‐Component Reaction Involving Isocyanide Insertion as a Key Step

A three‐component reaction involving isocyanides, o‐alkynyltrifluoroacetanilides, and amines for the efficient synthesis of 2‐substituted 1H‐indole‐3‐carboxamidines has been developed. The reaction proceeds through intramolecular aminopalladation of alkynes activated by isocyanide‐ligated palladium(II) species. Dioxygen acts as the sole oxidant to regenerate the active palladium(II) species.

     

Highly Enantioselective Michael Addition of α‐Substituted Cyano Ketones to β,γ‐Unsaturated α‐Keto Esters using Bifunctional Thiourea‐Tertiary Amine Catalysts: An Easy Access to Chiral Dihydropyrans

An asymmetric Michael addition of α‐substituted cyano ketones to β,γ‐unsaturated α‐keto esters to form chiral dihydropyrans catalyzed by a series of α‐amino acid‐derived thiourea‐tertiary amines is presented. A novel tyrosine‐derived thiourea catalyst was identified as the optimal catalyst providing the desired product in 91–95% yields and with 90–96% ee at a low catalyst loading of 2.0 mol%. The utility of the reaction was exemplified by facile conversion of the dihydropyran product into pharmaceutically useful dihydropyridine.     

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.

     

Ruthenium‐Catalyzed Synthesis of Secondary Alkylamines: Selective Alkylation with Aliphatic Amines

The chemoselective N‐alkylation of tert‐alkylamines applying aliphatic amines is described for the first time. In the presence of the Shvo catalyst 1 , tert‐octylamine 4 and 1‐adamantylamine 5 are alkylated using primary, secondary, and even tertiary amines to give the corresponding monoalkylated tert‐alkylamine in moderate to very good yields and excellent selectivity. This novel reaction proceeds without an additional hydrogen source and ammonia is formed as the only by‐product.     

Improved Turnover Numbers in Palladium‐Catalyzed Bisdiene Cyclization‐Trapping using N‐Heterocyclic Carbene Ligands

An optimized palladium‐N‐heterocyclic carbene catalyst system effects the palladium‐catalyzed bisdiene cyclization‐trapping with phenol at the 0.01% catalyst loading level with a TON of 7.6×10³ and TOF of 280 h⁻¹, values much higher than typically found for this and related carbocyclizations. The reaction scales well and the trans‐substituted six‐membered ring product is obtained in excellent yield on a 10‐mmole scale without further optimization of the catalyst system or reaction conditions.     

Highly Efficient Ligands for the Palladium‐Assisted Double N‐Arylation of Primary Amines for One‐Sep Construction of Carbazoles

A highly efficient one‐pot synthesis of carbazoles via palladium‐catalyzed double N‐arylation of primary amines with 2,2′‐dihalobiphenyls is described using a catalyst system comprised of tris(dibenzylideneacetone)dipalladium(0) (Pd₂dba₃) and the proazaphosphatrane P(i‐BuNCH₂CH₂)₃N ( 8 ) or its derivative (t‐Bu)₂PN P(i‐BuNCH₂CH₂)₃N ( 9a ) as the ligand. The process is effective for double N‐arylation of 2,2′‐biphenyl dibromide, diiodide, and even dichloride with a variety of primary amines including neutral, electron‐rich, electron‐deficient, and sterically hindered anilines as well as aliphatic amines.     

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.     

Generation of 11‐Fluoro‐11H‐indeno[1,2‐c]quinolines via a Palladium‐Catalyzed Three‐Component Reaction of 2‐Alkynylbromobenzenes, 2‐Alkynylanilines,and N‐Fluorobenzenesulfonimide

A novel and efficient synthesis of 11‐fluoro‐11H‐indeno[1,2‐c]quinolines has been developed via a palladium‐catalyzed three‐component reaction of 2‐alkynylbromobenzenes, 2‐alkynylanilines, and N‐fluorobenzenesulfonimide. The reaction works well with high selectivity. Additionally, the diversity and complexity could be easily introduced via a simple operation from readily available starting materials. In the meantime, a fluorine atom could be incorporated into the scaffold during the reaction process.     

Palladium‐Catalyzed Regioselective and Stereoselective Oxidative Heck Arylation of Allylamines with Arylboronic Acids

A general and convenient palladium‐catalyzed oxidative Heck arylation of both N‐protected and N,N‐diprotected allylic amines with arylboronic acids under mild conditions has been developed. The catalyst system, consisting of Pd(OAc)₂ (palladium acetate), AgOAc (silver acetate) and KHF₂ (potassium hydrogen fluoride), could efficiently catalyze the coupling reaction in acetone without the aid of any ligand, leading exclusively to the γ‐arylated allylic amine products in good to excellent yields. This method is highlighted with excellent regio‐ and stereocontrol and remarkable functional group tolerance. The carbamate moiety in allylic amine substrates is of crucial importance to the catalytic performance, and the chelation between the carbonyl O (oxygen) and Pd (palladium) atoms is believed to be responsible for the high regioselectivity and stereoselectivity observed.     

Preparation and characterization of new optically active poly(amide‐imide)s derived from N,N‐(4,4′‐Oxydiphthaloyl)‐bis‐(s)‐(+)‐valine diacid chloride and aromatic diamines

4,4′‐Oxydiphthalic anhydride (1) was reacted with (s)‐(+)‐valine (2) in acetic acid and the resulting imide‐acid 3 was obtained in high yield. This compound 3 was converted to diacid chloride 4 by reaction with excess amount of thionyl chloride. The polycondensation reaction of diacid chloride 4 with several aromatic diamines such as 4,4′‐sulfonyldianiline (5a), 4,4′‐diaminodiphenyl methane (5b), 4,4′‐diaminodiphenylether (5c), p‐phenylenediamine (5d), m‐phenylenediamine (5e), and 4,4′‐diaminobiphenyl (5f) was performed by two conventional methods: low temperature solution polycondensation and a short period reflux conditions. To compare conventional solution polycondensation reaction methods with microwave‐assisted polycondensation, the reactions were also carried out under microwave conditions in the presence of small amount of o‐cresol that acts as a primary microwave absorber. The reaction mixture was irradiated for 4 min with 100% of radiation power. Several new optically active poly(amide‐imide)s with inherent viscosity ranging from 0.26–0.44 dL/g were obtained with high yield. All of the above polymers were fully characterized by ¹H‐NMR, FTIR, elemental analyses, and specific rotation techniques. Some structural characterizations and physical properties of these new optically active poly (amide‐imide)s are reported. POLYM. ENG. SCI. 46:558–565, 2006. © 2006 Society of Plastics Engineers     

Preparation,property characterization and UV‐converting application of poly(conjugated azomethine‐urethane)/hydroxyl polyacrylate resin

A functional polyurethane coating with ultraviolet (UV) rays converting ability of changing higher energy UV rays into lower ones was prepared from poly(conjugated azomethine‐urethane) (CAUP) reacting with hydroxyl polyacrylate resin (HPAR). As an oligomeric isocyanate, CAUP was prepared in a reaction of toluene‐2,4‐diisocyanate with N,N′‐bis(4‐hydroxyl‐3‐methoxybenzylidene)‐o, m or p‐diaminobenzene that was synthesized from vanillin and o‐phenylenediamine or m‐phenylenediamine or p‐phenylenediamine. Fourier transform infrared spectroscopy, ¹H‐NMR, UV–vis, and fluorescence spectra were used to characterize those synthesized products and HPAR/CAUP films. UV‐converting abilities of HPAR/CAUP films had been demonstrated by natural exposure to ageing and the fluorescence emission spectra of HPAR/CAUP films and CAUP solutions. Red‐shift phenomena in the fluorescence emission spectra were due to molecule aggregations and stacks caused by intramolecular and intermolecular interactions such as hydrogen bonding effects. Dynamic mechanical thermal analysis and thermogravimetric analysis techniques were employed to study their mechanical and thermal properties of HPAR/CAUP films. The films exhibited excellent mechanical properties and owned high glass transition temperatures over 97.0°C, and their maximum thermal degradation temperatures were about 176.0°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Regioselective Heck Reaction of N‐Vinylphthalimide: A General Strategy for the Synthesis of (E)‐N‐Styrylphthalimides and Phenethylamines

The arylation of N‐vinylphthalimide takes place at the β‐position with aryl iodides, bromides and chlorides using palladium acetate [Pd(OAc)₂] or phenone oxime‐derived palladacycles as catalysts under phosphine‐free conditions. The reaction is succesfully carried out in organic solvents, such as DMF, in the presence of an organic base, such as dicyclohexylmethylamine, and with TBAB as additive at 120 °C under conventional or microwave heating. (E)‐N‐Styrylphthalimides are mainly obtained using a rather low palladium loading (0.05–1 mol%). Similar catalytic efficiency is observed using a Kaiser oxime resin‐derived palladacycle, which allows reuse of the polymeric complex for three cycles. The high regioselectivity observed supports that these palladacycles work as a source of Pd(0) species operating mainly through a neutral mechanism. The syntheses of 2‐thienylphenethylamine and mescaline have been performed by subsequent hydrogenation with Wilkinson’s catalyst and hydrazinolysis.     

Palladium on Charcoal as a Recyclable Catalyst for C?S Cross‐Coupling of Thiols with Aryl Halides under Ligand‐Free Conditions

S‐Arylation of a wide variety of substituted aryl and aliphatic thiols with aryl halides using a catalytic amount of palladium on charcoal as a heterogeneous catalysis with potassium hydroxide as the base in dimethyl sulfoxide (DMSO) at 110 °C is accomplished in good yields. The C S bond formation reaction functions under ligand‐free conditions, and the palladium on charcoal catalyst can be is reused for five runs without any loss of activity.     

A Further Decrease in the Catalyst Loading for the Palladium‐Catalyzed Direct Intramolecular Arylation of Amides and Sulfonamides

The direct arylation of N‐substituted o‐bromobenzanilides and benzenesulfonamides via C H bond functionalization has been developed using very low catalyst loadings. This novel cost‐effective and more sustainable method relies on a PCN‐type palladium pincer complex as a highly active palladium source, providing a general and efficient access to phenanthridinones, biaryl sultams and related heterocyclic systems. The beneficial effect of water as cosolvent has been observed in this process, which is not seriously influenced by electronic effects at the arene moieties or sterically demanding substituents at the amide or sulfonamide nitrogen. In addition, a number of experiments (kinetic plot, poisoning assays, TEM, ESI) have been performed in order to understand the role of the employed palladium complex in this reaction.

     

Convenient synthesis of sulfonamides from amines and p‐toluene sulfonyl chloride mediated by crosslinked poly(4‐vinylpyridine)

A general, mild, and convenient method has been developed for the synthesis of various N‐substituted and N, N‐disubstituted sulfonamides, as a class of sulfa drugs, from the corresponding amines and p‐toluene sulfonyl chloride in the presence of readily available crosslinked poly(4‐vinylpyridine) as a catalyst, base or polymeric substrates. The use of polymeric catalyst simplifies routine sulfonylation of amines because it eliminates the traditional purification. The polymer can be removed quantitatively and it can be regenerated and reused for several cycles without losing its activity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012