Visible light-mediated photocatalytic bromination of 2-arylimidazo[1,2-a]pyridines using CBr4 as bromine source

Abstract

The photocatalytic bromination of 2-arylimidazo[1,2-a]pyridines is described in this paper. This reaction uses the readily accessible and shelf-stable CBr₄ as a bromine source. This photocatalytic system is shown to serve as a convenient and practical synthetic protocol for the preparation of 2-aryl-3-bromoimidazo[1,2-a]pyridines.     

Derivatives of benzo[5,6]cyclohepta[1,2-b]thiophene. Synthesis of 2,3,7,8-tetrahydro-3-oxothieno[1,2-b]cyclohepta[5,6,7-de]isoquinoline and 1,2,3,7,8,11b-hexahydro-3-oxothieno[1,2-b]cyclohepta[5,6,7-de]isoquinoline

The synthesis of the title compounds was carried out by cyclization via isocyanate of (E)-4,5-dihydro-10H-benzo[5,6]cyclohepta[1,2-b]-thiophene-10-ylideneacetic acid and 4,5-dihydro-10H-benzo[5,6]cyclohepta[1,2-b]-thiophene-10-ylacetic acid respectively, which were obtained by the Wadsworth-Emmons modification of the Wittig reaction of 4,5-dihydro-10H-10-oxobenzo[5,6]cyclohepta[1,2-b]thiophene and triethyl phosphonacetate. The structures of these new compounds are described.     

Indium(III)chloride catalyzed synthesis of novel 1H-pyrazolo[1,2-b]phthalazine-5,10-diones and 1H-pyrazolo[1,2-a]pyridazine-5,8-diones under solvent-free condition

An efficient, inexpensive and environmentally friendly synthesis of novel 3-amino-2-benzoyl-1-aryl-1H-pyrazolo[1,2-b]phthalazine-5,10-dione and 3-amino-2-benzoyl-1-aryl-1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives has been developed via one-pot three-component reaction of phthalhydrazide or maleic hydrazide, aldehydes and arylacetonitrile in the presence of catalytic amount of InCl₃ as a Lewis acid catalyst under solvent-free conditions. The most important features of the present protocol are mild reaction conditions, short reaction times, high yields, and a wide range of functional group tolerance.     

Synthesis of novel imidazo[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepines and pyrimido[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepines

Several 1 1-amino-5H-pyrrolo[2,1-c][1,4]benzodiazepines have been used as starting material to prepare a number of derivatives of 9H-imidazo[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepines and 10H-pyrimido[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepines. The imidazole nucleus was built by reaction of amidines with ethyl bromopyruvate or aminoacetaldehyde dimethylacetal. Several derivatives of imidazo[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepine have been prepared by formylation of the pyrrole ring followed by formation of thioamides. Condensation of 11-amino-5H-pyrrolo[2,1-c][1,4]benzodiazepines with diethyl ethoxymethylenemalonate afforded intermediate diesters which were transformed into the corresponding 10H-pyrimido[1,2-a]pyrrolo[2,1-c]-benzodiazepines.     

1,2,4-Triazines. VI. Imidazo[1,2-b]-as-triazines

Imidazo[1,2-b]-as-triazines were obtained in high yields by heating substituted glyoxaldoximes with 1,2-diaminoimidazoles in the presence of hydrochloric acid. Phenylglyoxal hydrate in a similar reaction afforded a mixture of 2- and 3-diphenyl-6-arylimidazo[1,2-b]-as-triazines. α-Ketoacids and 1,2-diaminoimidazoles in the presence of hydrochloric acid afforded 2,6-disubstituted-4H-imidazo[1,2-b]-as-triazin-3-ones.     

Catalyst-free synthesis of novel 4H-indeno[1,2-b]furan-4-ones and furo[2,3-d]pyrimidines in water

An operationally simple, catalyst-free, and efficient protocol for the synthesis of novel 4H-indeno[1,2-b]furan-4-one and furo[2,3-d]pyrimidine derivatives by a one-pot reaction of 2-aminopyridines, 1,3-indandione, or barbituric acid and phenylglyoxal monohydrate in water at reflux, involving domino aldol condensation, Michael addition, and ring-closing reactions is described. This transformation has several advantages, including high yield, short reaction duration, simple workup, and simple purification.     

Ring closure reactions with nitriles. I. Formation of pyrrolo [2,1-c] [1,2,4] benzothiadiazines and pyrrolo[1,2-a] quinazolines

Pyrrolo[2,1-c][1,2,4]benzothiadiazines have been prepared from the reactions of o-amino-benzenesulfonamides with γ-cyanopropionaldehydes. Pyrrolo[1,2-a]quinazolines have been prepared from the reaction of anthranilamides with either γ-cyanopropionaldehyde or succinic anhydride. The cyclization of a 4-oxo-2-quinazolinepropionic acid has produced a pyrrolo-[1,2-a]quinazoline and the isomeric pyrrolo[2,1-b]quinazoline.     

Carbon-SO3H catalyzed expedient synthesis of new spiro-[indeno[1,2-b]quinoxaline-[11,2′]-thiazolidine]-4′-ones as biologically important scaffold

In this report, we have described a convenient and eco-compatible approach for synthesis of new hybrid spiro[indeno[1,2-b]quinoxaline-[11,2′]-thiazolidine]-4′-ones (4a–k) via multi-component reaction of indeno[1,2-b]quinoxalinone, α-mercaptocarboxylic acids and various types of amines using urea-choline chloride as green deep eutectic solvent and carbon-SO₃H as a solid acid catalyst. This new protocol produces a thiazolidine ring attached to indeno[1,2-b]quinoxaline through spiro carbon in good to excellent yields. The advantages of this protocol are avoidance of toxic and harmful catalyst and solvents further both catalyst and DES were recovered from the reaction mixture quantitatively and reused several times. Synthesized compounds were characterized on the basis of spectral and single crystal X-ray analysis. The prepared catalyst was characterized by FT-IR, SEM, and X-ray diffraction method.     

Polycyclic N-hetero compounds. XXXV. Syntheses and anti-platelet aggregation activity of 5,6-Dihydro-4H-benzo[3,4]cyclohept[1,2-e]imidazo[1,2-c]pyrimidines with an oxygen function at the 1-position

Various 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-d][pyrimidines bearing amino acid group at the 4-position of the skeleton were synthesized by the reaction of 4-chloro-6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-d]-pyrimidine with some amino acid, which were cyclized to 5,6-dihydro-4H-benzo[3,4]cyclohept[1,2-e]imidazo-[1,2-c]pyrimidines, corresponding to B-homo-11,13,15-triazasteroids. Their inhibitory activities against platelet aggregation induced by collagen were also investigated.     

Green procedure for highly efficient,rapid synthesis of imidazo[1,2-a]pyridine and its late stage functionalization

We unfold a rapid synthetic protocol for the preparation of imidazo[1,2-a]pyridine in cyclohexane. This methodology includes several advantages like shorter reaction time, catalyst free, broader substrate scope, and good yields of the desired products. Late stage functionalization of imidazo[1,2-a]pyridine has also been performed through C–H bond activation and C–C cross-coupling reactions.     

Syntheses of 10-Oxo-10H-pyrido[1,2-a]thieno[3,4-d]pyrimidines and 10-Oxo-10H-pyrido[1,2-a]thieno[3,2-d]pyrimidines from methyl tetrahydro-4-oxo-3-thiophenecarboxylate and methyl tetrahydro-3-oxo-2-thiophenecarboxylate,respectively

A general synthesis of 10-Oxo-10H-pyrido[1,2-a]thieno[3,4-d]pyrimidines and 10-Oxo-10H-pyrido[1,2-a]-thieno[3,2-d]pyrimidines is described. Methyl tetrahydro-4-oxo-3-thiophenecarboxylate ( 13 ) was condensed with 6-aminonicotinic acid ( 18 ) to give 3,10-dihydro-10-oxo-1H-pyrido[1,2-a]thieno[3,4-d]pyrimidine-7-carboxylic acid ( 19 ). Treatment of 19 successively with chlorotrimethylsilane, N-chlorosuccinimide and water gave 10-oxo-10H-pyrido[1,2-a]thieno[3,4-d]pyrimidine-7-carboxylic acid ( 17 ). Methyl tetrahydro-3-oxo-2-thiophenecarboxylate ( 21 ) was converted to 10-oxo-10H-pyrido[1,2-a]thieno[3,2-d]pyrimidine-7-carboxylic acid ( 25 ) by an analogous route.     

Formation of Heptaleno[1,2-c]furans and Heptaleno[1,2-c]furanones

The dehydrogenation reaction of the heptalene-4,5-dimethanols 4a and 4d , which do not undergo the double-bond-shift (DBS) process at ambient temperature, with basic MnO₂ in CH₂Cl₂ at room temperature, leads to the formation of the corresponding heptaleno[1,2-c]furans 6a and 6d , respectively, as well as to the corresponding heptaleno[1,2-c]furan-3-ones 7a and 7d , respectively (cf. Scheme 2 and 8). The formation of both product types necessarily involves a DBS process (cf. Scheme 7). The dehydrogenation reaction of the DBS isomer of 4a , i.e., 5a , with MnO₂ in CH₂Cl₂ at room temperature results, in addition to 6a and 7a , in the formation of the heptaleno[1,2-c]-furan-1-one 8a and, in small amounts, of the heptalene-4,5-dicarbaldehyde 9a (cf. Scheme 3). The benzo[a]heptalene-6,7-dimethanol 4c with a fixed position of the C?C bonds of the heptalene skeleton, on dehydrogenation with MnO₂ in CH₂Cl₂, gives only the corresponding furanone 11b (Scheme 4). By [²H₂]-labelling of the methanol function at C(7), it could be shown that the furanone formation takes place at the stage of the corresponding lactol [3-²H₂]- 15b (cf. Scheme 6). Heptalene-1,2-dimethanols 4c and 4e , which are, at room temperature, in thermal equilibrium with their corresponding DBS forms 5c and 5e , respectively, are dehydrogenated by MnO₂ in CH₂Cl₂ to give the corresponding heptaleno[1,2-c]furans 6c and 6e as well as the heptaleno[1,2-c]furan-3-ones 7c and 7e and, again, in small amounts, the heptaleno[1,2-c]furan-1-ones 8c and 8e , respectively (cf. Scheme 8). Therefore, it seems that the heptalene-1,2-dimethanols are responsible for the formation of the furan-1-ones (cf. Scheme 7). The methylenation of the furan-3-ones 7a and 7e with Tebbe's reagent leads to the formation of the 3-methyl-substituted heptaleno[1,2-c]furans 23a and 23e , respectively (cf. Scheme 9). The heptaleno[1,2-c]furans 6a, 6d , and 23a can be resolved into their antipodes on a Chiralcel OD column. The (P)-configuration is assigned to the heptaleno[1,2-c]furans showing a negative Cotton effect at ca. 320 nm in the CD spectrum in hexane (cf. Figs. 3–5 as well as Table 7). The (P)-configuration of (–)- 6a is correlated with the established (P)-configuration of the dimethanol (–)- 5a via dehydrogenation with MnO₂. The degree of twisting of the heptalene skeleton of 6 and 23 is determined by the Me-substitution pattern (cf. Table 9). The larger the heptalene gauche torsion angles are, the more hypsochromically shifted is the heptalene absorption band above 300 nm (cf. Table 7 and 8, as well as Figs. 6–9).     

A new synthetic approach for imidazo[1,2-a]imidazoles and pyrrolo[1,2-a]imidazoles

Substituted pyrrolo[1,2-a]imidazoles and imidazo[1,2-a]imidazoles are prepared in a simple one pot reaction sequence from esters of heterocyclic or aromatic α-amino acids. The reaction involves condensation with acetoine followed by cyclization with either malonodinitrile, ethyl cyanoacetate or cyanamide.     

Formylation of 3,4-Dihydropyrrolo[1,2-a]pyrazines

Formylation of 3,4-dihydropyrrolo[1,2-a]pyrazines containing alkyl or aryl substituents at position 1 has been studied under the conditions of the Vilsmeier reaction. The direction of the reaction depends on the structure of 3,4-dihydropyrrolo[1,2-a]pyrazine starting materials. Formylation of 1-methyl-substituted 3,4-dihydropyrrolo[1,2-a]pyrazines occurs at the methyl group.     

Synthesis of Substituted Indolo[1,2- a ]quinoxalines

Abstract

1-(2-Nitrophenyl)indole-2-carboxylates 5, obtained by the N-arylation of indole-2-carboxylates 4, on catalytic reductive cyclization afford indolo[1,2-a]quinoxalino-6(5H)-ones 6. These compounds on reduction with LAH in ether/THF yielded indolo[1,2-a]quinoxalines 7.     

Synthesis of seven- and eight-membered [1,2-a] alicyclic ring-fused benzimidazoles and 3-aziridinylazepino[1,2-a]benzimidazolequinone as a potential antitumour agent

Azepino and azocino[1,2-a]benzimidazoles were obtained either by treatment of 1-nitrophenyl-2-azacycloalkanes via a one-pot catalytic hydrogenation/acetylation or by treatment of the acetamides generated in the latter reaction with performic acid. This represents the first facile synthesis of eight-membered [1,2-a] alicyclic ring-fused benzimidazoles. 3-Methoxy-azepino[1,2-a]benzimidazole was elaborated to the novel potential cytotoxin, 3-(N-aziridinyl)-7,8,9,10-tetrahydro-6H-azepino[1,2-a]benzimidazole-1,4-dione. The synthesis included clarification of the reactivity of methoxy-substituted benzimidazoles towards nitration.     

Polycyclic N-hetero compounds. XIX. Synthesis of novel meso-ionic benz[h]imidazo[1,2-c]quinazoline and benzo[h]pyrrolo[1′,2′:3,4]imidazo[1,2-c]quinazoline derivatives

Benz[h]imidazo[1,2-c]quinazolinium-l-olate (5) and benzo[h]pyrrolo[1′,2′:3,4]imidazo[1,2-c]quinazolinium-8-olate (9) having novel meso-ionic ring systems were synthesized by the reaction of N-(5,6-dihydrobenzo[h]-quinazolin-4-yl)amino acids with acetic anhydride.     

Pd-catalyzed oxidative cross-coupling of imidazo[1,2-a]pyridine with arenes

A facile method for direct Pd(OAc)₂-catalyzed oxidative cross-coupling of unactivated imidazo[1,2-a]pyridine with simple arenes has been developed. The reaction shows good reaction efficiency, high regioselectivity, and good functional-group compatibility. This approach provides a useful protocol for the preparation of imidazo[1,2-a]pyridine–arene structure of interest in biological and pharmaceutical materials.     

Dipyrrolo[1,2-a:2',1'-c]pyrazines. 8. Electrophilic Substitution in Dipyrrolo[1,2-a:2',1'-c]pyrazines and 5,6-Dihydrodipyrrolo[1,2-a:2',1'-c]pyrazines. Acylation of Dipyrrolo[1,2-a:2',1'-c]pyrazines

Esters, nitriles, and amides of dipyrrolo[1,2-a:2',1'-c]pyrazines have been synthesized by the acylation of dipyrrolo[1,2-a:2',1'-c]pyrazines and 5,6-dihydrodipyrrolo[1,2-a:2',1'-c]pyrazines with trichloroacetic acid chloride, p-tosyl isocyanate, and isocyanatophosphoric acid dichloride (Kirsanov isocyanate).     

Ag2Cr2O7 nanoparticles: An eco-friendly and reusable catalyst for synthesis of pyrano[c]chromenediones and [1,3]dioxolo[g]chromeneones in aqueous media at ambient temperature

An efficient and green protocol for the synthesis of 4-aryl-3,4-dihydro-2H,5H-pyrano[3,2-c]chromene-2,5-diones and 8-aryl-7,8-dihydro-6H-[1,3]dioxolo[4,5-g]chromene-6-ones through the Ag₂Cr₂O₇ nanoparticles catalyzed cyclocondensation reaction of active methylene compounds including 4-hydroxycoumarin or 3,4-methylenedioxyphenol, aromatic aldehydes, and meldrum's acid in water at ambient temperature was described. This method demonstrates several advantages compared with methods that are currently employed such as a mild reaction conditions, simple work-up, good to excellent yields, avoiding toxic catalyst and hazardous solvent, and recovery and reuse of the catalyst.