An effective new synthesis of 2-aminopyrrole-4-carboxylates

Efficient syntheses of 2-aminopyrroles are presented starting from β-dicarbonyl compounds, bromoacetonitrile, and amines. Alkylation of β-dicarbonyl compounds with bromoacetonitrile furnished α-cyanomethyl-β-dicarbonyl compounds. The condensation reaction of α-cyanomethyl-β-dicarbonyl compounds with amines catalyzed by p-TsOH affords the corresponding enamines in good yields. Base catalyzed cyclization via the addition of an amine moiety to the carbon-nitrogen triple bond of nitrile furnished 2-aminopyrroles in high yields.     

Pd2dba3/P(i-BuNCH2CH2)3N: a highly efficient catalyst for the one-pot synthesis of trans-4-N,N-diarylaminostilbenes and N,N-diarylaminostyrenes

A Pd₂dba₃/P(i-BuNCH₂CH₂)₃N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners.     

An efficient synthesis of 4,5-dihydronaphtho[2,1-b]furan through a novel ring transformation of 2H-pyran-2-one

An innovative route for the synthesis of substituted naphtho[2,1-b]furan has been delineated through a ring transformation reaction of suitably functionalized 2H-pyran-2-ones by reaction with 6,7-dihydro-5H-benzofuran-4-one, in good yield.     

l-Proline catalyzed efficient and convenient synthesis of substituted 2H-chromenes by three-component reaction

A convenient and efficient method is described for the synthesis of alkoxy substituted 2H-chromens by l-proline catalyzed reaction of salicylaldehydes with diketone in alcohol. The method is applicable for various substituted salicylaldehydes and aliphatic as well as benzylic alcohols.     

Suzuki reaction on pyridinium N-(5-bromoheteroar-2-yl)aminides

The reactivity of substituted pyridinium N-(2′-azinyl)aminides in Suzuki-Miyaura cross-coupling reaction is reported. The reaction proceeds in good yield employing Cs₂CO₃ as base, and producing substitution on the negatively charged moiety.     

Synthesis of substituted thiazolo[4,5-b]pyridines and other annulated heterocycles via SN2→Thorpe-Ziegler→Thorpe-Guareschi domino reactions

A new combinatorial method for the preparation of substituted thiazolo[4,5-b]pyridines, which utilizes cyanoacetamide, heterocumulenes (isothiocyanates, carbon bisulfide), and ethyl-4-chloroacetoacetate in a new S_N2→Thorpe-Ziegler→Thorpe-Guareschi domino reactions has been developed. The obtained thiazolo[4,5-b]pyridines were then used together with aldehydes and malononitrile in another Knoevenagel reaction→Michael reaction→hetero-Thorpe-Ziegler domino reaction for the synthesis of substituted 4,6-dihydro-5H-pyrano[2,3-d]thiazolo[4,5-b]pyridines.     

Eco-friendly and facile synthesis of 2-substituted-1H-imidazo[4,5-b]pyridine in aqueous medium by air oxidation

We report a new environmentally-benign, convenient, and facile methodology for the synthesis of 2-substituted-1H-imidazo[4,5-b]pyridine. The reaction of 2,3-diaminopyridine with substituted aryl aldehydes in water under thermal conditions without the use of any oxidative reagent has been studied. The reaction has yielded 1H-imidazo[4,5-b]pyridine derivatives by an air oxidative cyclocondensation reaction in one step in an excellent yield. Furthermore, a series of compounds were synthesized and characterized by melting point, EI-MS, NMR, and IR tools. For comparison, the reference samples were prepared by the reported method. Utilization of aqueous medium, easy reaction conditions, isolation, and purification make this manipulation very interesting from an economic and environmental perspective.     

A concise synthesis of novel naphtho[a]carbazoles and benzo[c]carbazoles

Starting from simple indole precursors the synthesis of naphtho[a]carbazoles and benzo[c]carbazoles is described. Key steps include the use of the Suzuki-Miyaura reaction to afford 2- or 3-aryl substituted indoles, as well as a potassium t-butoxide and light assisted aromatic ring-forming reaction.     

Reaction of difluorocarbene with anions from amides and oximes: Synthesis of N-difluoromethyl substituted amides, O-difluoromethylimidates or O-difluoromethyl substituted oximes under phase-transfer catalysis conditions

N-Aryl substituted amides react with chlorodifluoromethane in the presence of concentrated aqueous sodium hydroxide and benzyltriethylammonium chloride (TEBAC) as a catalyst in benzene (phase-transfer catalysis, PTC), affording mixtures of N- and O-difluoromethyl substituted derivatives. Amide anions are involved in this process. The reaction carried out with oximes gives O-difluoromethyl oxime ethers.     

A new approach to the synthesis of 4-(N-aryl)carbamoylmethyl-4,5-dihydropyridazin-3(2H)-ones

Reaction of N-aryl substituted maleimides with aliphatic ketazines leads to the formation of 4,5-dihydropyridazin-3(2H)-ones in moderate yields. The reaction proceeds through 1,4-addition of an azine to the maleimide double bond, as confirmed by separation of the corresponding adducts in some cases, which are then converted into 4,5-dihydropyridazin-3(2H)-ones. In addition, the solid-state synthesis of 4,5-dihydropyridazin-3(2H)-ones is demonstrated for the first time.     

Effect of the leaving group on the reaction of 2-aminopyrroles with electron deficient heteroaromatic azadienes: substitution by addition-elimination versus cycloaddition

When a good leaving group is present in the heteroaromatic azadiene, reaction with 2-aminopyrroles occurs by substitution by addition-elimination instead of cycloaddition. This novel reaction is sensitive to steric effects and takes place in 2-amino-1-methylpyrrole at C-5 and the exo amino group but at C-3 in 2-amino-1-t-butylpyrrole.     

A concise synthesis of asymmetrical N,N′-disubstituted guanidines

We present a new and concise method for the preparation of asymmetrical N,N′-disubstituted guanidines starting from thiourea via the reaction of N-Boc-protected N′-alkyl/aryl substituted thioureas with an amine in the presence of mercury(II) chloride and triethylamine.     

Microwave-assisted one-pot synthesis of benzo[b][1,4]thiazin-3(4H)-ones via Smiles rearrangement

The synthesis of benzo[b][1,4]thiazin-3(4H)-one derivatives in a simple and efficient method from the one-pot reaction of substituted 2-chlorobenzenthiols, chloroacetyl chloride, and primary amines via Smiles rearrangement under microwave irradiation gave high yields (65-92%) of the products with short reaction time (15-20 min).     

Pd/C mediated synthesis of 2-substituted benzo[b]furans/nitrobenzo[b]furans in water

An efficient synthesis of 2-alkyl/aryl substituted benzo[b]furans/nitrobenzo[b]furans in water has been accomplished via Pd/C catalyzed reaction of o-iodophenols with terminal alkynes in the presence of PPh₃, CuI and prolinol. This method can tolerate a variety of functional groups present in the alkynes as well as base labile nitro group in the o-iodophenols. The protocol does not require the use of a phase transfer catalyst or water-soluble phosphine ligands and is free from the use of any organic co-solvent.     

Dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes with lanthanum metal

It was found that lanthanum metal caused the dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes to generate the corresponding benzynes and o-quinodimethanes. When o-dihalogen substituted arenes were allowed to react with lanthanum metal in the presence of dienes, the Diels-Alder products between benzyne and dienes were formed in moderate to good yields. Similarly, the Diels-Alder adducts of o-quinodimethane with dienophiles were obtained, in the reaction of α,α′-dibromo-o-xylenes with lanthanum metal in the presence of dienophiles.     

Concise synthesis of multiply substituted stereodefined cis,cis-2,4-diene-1,6-dials, cis,cis-2,4-diene-1,6-diols and further applications

Reactions of 1,4-dilithio-1,3-dienes with DMF afforded multiply substituted stereodefined cis,cis-2,4-diene-1,6-dials in high yields. Treatment of these 1,6-dials with LiAlH₄ or RLi resulted in the formation of their corresponding 1,6-diols. These bifunctional compounds, cis,cis-2,4-diene-1,6-dials and -1,6-diols are otherwise not readily available. Further reaction of these 1,6-diols with an aldehyde catalyzed by strong acids led to the formation of oxacycles of novel structures.     

Synthesis of fully substituted pyrazolo[3,4-b]pyridine-5-carboxamide derivatives via a one-pot four-component reaction

A one-pot four-component reaction of an aliphatic or aromatic amine, diketene, an aromatic aldehyde and 1,3-diphenyl-1H-pyrazol-5-amine in the presence of p-toluenesulfonic acid as a catalyst has been developed. In this reaction, a new class of fully substituted pyrazolo[3,4-b]pyridine-5-carboxamide derivatives is produced under mild reaction conditions and in good yields at ambient temperature.     

Catalyst-free synthesis of functionalized dihydro-2-oxypyrroles by the reaction of enaminones and N,N′-bis(phenylmethylidene)phenylmethane

A catalyst-free and convenient approach for the preparation of substituted dihydro-2-oxypyrrole is described. This three-component reaction between primary amines, dialkyl acetylenedicarboxylate, and N,N′-bis(phenylmethylidene)phenylmethane proceeds in MeOH under reflux conditions in good to excellent yields.     

A new entry to the substituted pyrrolo[3,2-c]quinoline derivatives of biological interest by intramolecular heteroannulation of internal imines

New 1,3,4-substituted pyrrolo[3,2-c]quinoline derivatives were synthesised in good yields by oxidative heteroannulation of internal imines starting from easily prepared substituted 5-(2-aminophenyl)pyrroles and commercially available aryl and heteroaryl aldehydes. The reaction occurs as a one-pot process involving an intramolecular acid catalysed reaction.     

Regioselective synthesis of functionalized naphtho[b]thiophenes through a ‘lactone methodology’

Benzo[b]thiophene and its benzannulated derivatives are important classes of compounds due to their unique chemical properties and biosteric relationship with indole. In this letter, we report a convenient route for the synthesis of substituted naphtho[b]thiophenes through a ring transformation reaction of suitably functionalized 2H-pyran-2-ones with 6,7-dihydro-5H-benzothiophene-4-one, in good yields.