Some novel heterocyclic systems derived from 7-amino-2,3-dihydro-8-nitro-1H-pyrrolo[1,2-α]benzimidazole and the corresponding diamine

The preparation of 7-amino-2,3-dihydro-8-nitro-1H-pyrrolo[1,2-a]benzimidazole from 1,4-diacetamido-2,3-dinitrobenzene is described. Reaction of this compound with 2,5-dimethoxytetrahydrofuran produces 2,3-dihydro-8-nitro-7-N-pyrrolo-1H-pyrrolo[1,2-a]benzimidazole, which can be cyclised to produce two new heterocyclic ring systems, 9,10-dihydro-8H-pyrrolo[1,2-a]pyrrolo(1′,2′:1,2]imidazo[5,4-f]quinoxaline and 9,10-dihydro-8H-pyrrolo[2,1-c]pyrrolo[1′,2′:1,2]imidazo[4,5-h][1,2,4]benzotriazine. The corresponding diamine, 7,8-diamino-2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole undergoes a variety of condensation reactions to produce several new heterocyclic systems, for example, with formic acid, 1,7,8,9-tetrahydroimidazo-[4,5-e]pyrrolo[2,1-6]benzimidazole is formed and with diacetyl, 9,10-dihydro-2,3-dimethyl-8H-pyrrolo-[1′,2′:1,2]imidazo[5,4-y]quinoxaline is obtained.     

A novel and easy two-step,microwave-assisted method for the synthesis of halophenyl pyrrolo[2,3-b]quinoxalines via their pyrrolo precursors. Evaluation of their bioactivity

A novel, two-step, facile route for the synthesis of pyrrolo[2,3-b]quinoxalines via 2,3-dioxopyrroles, enhanced by microwave irradiation, is presented. The newly synthesized 2,3-dioxo-5-halophenyl pyrrolo precursors 4a–c as well as the non-aromatized ethyl 2-(4-halophenyl)-1-methyl-2,4-dihydro-1H-pyrrolo[2,3-b]quinoxaline-3-carboxylates 6a–c and the aromatized ethyl 2-(4-halophenyl)-1-methyl-1H-pyrrolo[2,3-b]quinoxaline-3-carboxylates 7a–c were evaluated for their antioxidant, cytostatic, and antiviral properties. Most of them proved to be potent hydroxyl radical scavengers and inhibited in vitro lipid peroxidation. The compounds showed moderate antiproliferative activity, while 6a inhibited vaccinia virus at an EC₅₀ value of 2 μM, and 4c and 6c inhibited Sindbis virus at EC₅₀ values of 4 μM.     

Pyrrolopyridine analogs of nalidixic acid. 1. Pyrrolo[2,3-b]pyridines

A series of 4,7-dihydro-4-oxo-1H-pyrrolo[2,3-b]pyridine-5-carboxylic acids was synthesized from ethyl 5-methyl(or 5H)-2-aminopyrrole-3-carboxylate. The starting pyrroles were obtained by reaction of carbethoxyacetamidine with bromoacetone or chloroacetaldehyde. One compound ( 10 ) showed antibacterial activity in vitro.     

Novel heterocyclic β-nitroenamines-based on a one-pot three-component reaction: a facile synthesis of fully substituted 1H-pyrrolo[1,2-a]-fused-1,3-diazaheterocycles

A one-pot multicomponent synthesis of a novel class of 2,3-dihydro-1H-pyrrolo[1,2-a]imidazoles, 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidines, and 2,3,4,5-tetrahydro-1H-pyrrolo[1,2-a][1,3]diazepines, starting from simple and readily available inputs including diveres diamines, l,l-bis(methylthio)-2-nitroethen and diaroylacetylene, in excellent yields is described.     

Unexpected synthesis of azepino[4,3,2-cd]indoles from 4-aminoindoles

Unexpected regioselectivity for the Skraup-Doebner-Von Miller reaction was observed during the synthesis of quinolines from 4-aminoindoles and acetone in the presence of hydrochloric acid as a catalyst. The products were unambiguously assigned as 1-alkyl-3,5,5-trimethyl-5,6-dihydro-1H-azepino[4,3,2-cd]indoles instead of 2,2,4-trimethyl-2,7-dihydro-1H-pyrrolo[2,3-h]quinolones based on NMR spectroscopy and X-ray crystallographic analysis.     

Building libraries of skeletally diverse scaffolds from novel heterocyclic active methylene compound through multi-component reactions

Libraries of skeletally diverse potential bioactive polycyclic/spirocyclic heterocyclic compounds; 2-amino-7,9-dimethyl-5-oxo-4-aryl-4,5,6,7-tetrahydropyrano[2,3-d]pyrazolo[3,4-b]pyridine-3-carbonitrile, 2′-amino-7′,9′-dimethyl-2,5′-dioxo-6′,7′-dihydro-5′H-spiro[indoline-3,4′-pyrano[2,3-d]pyrazolo[3,4-b]pyridine]-3′-carbonitrile, and 5,5′-(arylmethylene)bis(4-hydroxy-1,3-dimethyl-1H-pyrazolo[3,4-b]pyridin-6(7H)-one) have been synthesized through a multi-component reaction using novel heterocyclic active methylene compound 4-hydroxy-1,3-dimethyl-1H-pyrazolo[3,4-b]pyridine-6(7H)-one as one of the building blocks. This protocol can be considered to be an efficient and eco-friendly strategy for diversity oriented synthesis.     

Microwave assisted synthesis of 2,3-dihydro-4H-benzo[4,5]thiazolo[3,2-a]furo[2,3-d]pyrimidin-4-ones and 6,7-dihydro-5H-furo[2,3-d]thiazolo[3,2-a]pyrimidin-5-ones using Mn(OAc)3

2-Hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-one 2a and 7-hydroxy-5H-thiazolo[3,2-a]pyrimidin-5-one 2b, were obtained in high yields under mild conditions from the cyclization reactions of bis-(2,4,6-trichlorophenyl) malonate and 2-aminobenzothiazole or 2-aminothiazole, respectively. A new class of compounds, 2,3-dihydro-4H-benzo[4,5]thiazolo[3,2-a]furo[2,3-d]pyrimidin-4-ones and 6,7-dihydro-5H-furo[2,3-d]thiazolo[3,2-a]pyrimidin-5-ones, were synthesized via the microwave assisted radical addition of compounds 2a and 2b to various alkenes using manganese(III) acetate. A preliminary acetylcholine esterase (AchE) inhibition test of compound 4e showed excellent (92%) inhibitory potential, comparable with the standard drug Donapezil®.     

Synthesis of pyrroloazepines. Facile synthesis of 2-substituted pyrrole derivatives by the phosgene method

A highly convenient method for the synthesis of 2-substituted pyrrole derivatives 7a-c from pyrrole using phosgene was developed. Successively, 7-methyl-6,7-dihydro-1H,5H-pyrrolo[2,3-c]azepine-4,8-dione 1a and 6,7-dihydro-1H,5H-pyrrolo[2,3-c]azepine-4,8-dione 1b (aldisin) were synthesized by phosphorus pentoxide/methanesulfonate and polyphosphoric acid cyclization.     

A one-pot synthesis of 3-methyl-5-aryl-4H-pyrrolo[2,3-d]-isoxazoles

Sharpless epoxidation of 4-amino-3-methyl-5-styrylisoxazoles 1 resulted in the formation of 3-methyl-5-aryl-4H-pyrrolo[2,3-d]-isoxazoles 4 in a one-step reaction. The reaction initially involves epoxide formation, followed by ring-opening and cyclization. Finally dehydration leads to the title compounds. The pyrrolo[2,3-d]-isoxazoles 4 were also synthesized via an alternative procedure.     

Methyl 3,3,3-trifluoro-2-(thiazol-2-ylimino)propionate in cycloaddition and cyclocondensation reactions

The behavior of methyl 3,3,3-trifluoro-2-(thiazol-2-ylimino)propionate (1) in cycloaddition and cyclocondensation reactions was studied. Cycloaddition of dimethylcyanamide to imine 1 gave a thiazolo[3,2-a][1,3,5]triazine derivative. Cyclocondensations of imine 1 with 2-aminothiazoline, N-cyclohexylbenzamidine, methyl (Z)-3-aminobut-2-enoate, and 6-amino-1-benzyluracil yielded dihydroimidazo[2,1-b]thiazol-5(6H)-one, 4,5-dihydroimidazol-5-one, 4,5-dihydro-1H-pyrrol-5-one, and dihydro-1H-pyrrolo[2,3-d]pyrimidine-2,4,6-trione derivatives, respectively.     

Recyclization of 1,3-dialkyl-6-nitro-1<Emphasis Type="Italic">H</Emphasis>-imidazo[4,5-<Emphasis Type="Italic">b</Emphasis>]pyridine-2,5(3<Emphasis Type="Italic">H</Emphasis>,4<Emphasis Type="Italic">H</Emphasis>)-diones into imidazole derivatives

Treatment of 5-amino-1,3-dialkyl-2,3-dihydro-1H-imidazo[4,5-b]pyridin-2-ones with sodium nitrite in aqueous HCl gave 1,3-dialkyl-1H-imidazo[4,5-b]pyridine-2,5(3H,4H)-diones which were nitrated with potassium nitrate in sulfuric acid to 6-nitro derivatives, and the latter underwent recyclization into 4-amino-1,3-dialkyl-5-(1H-pyrazol-5-yl)-2,3-dihydro-1H-imidazol-2-ones by the action of hydrazine hydrate.     

Synthesis and some properties of N-unsubstituted pyrrolo[2,1-c]-1,3-diazacycloalkano[1,2-a]pyrazinones

Reactions of methyl 2-(2-formyl-1H-pyrrol-1-yl)alkanoates with unsubstituted aliphatic 1,2-, 1,3-, and 1,4-diamines gave N-unsubstituted pyrrolo[2,1-c]-1,3-diazacycloalkano[1,2-a]-pyrazinones. Some of them show ring-chain tautomerism. Transformations of these compounds led to a number of novel heterocyclic systems: 2,10-dihydro-3H,5H-imidazo[1,2-a]-pyrrolo[1,2-d]pyrazines, 2,3,4,11-tetrahydro-6H-pyrrolo[1??,2??:4,5]pyrazino[1,2-a]pyrimidines, 1,2,3,5,6,10b-hexahydroimidazo[1,2-a]pyrrolo[2,1-c]pyrazines, 1,3,4,6,7,11b-hexahydro-2H-pyrrolo[2??,1??:3,4]pyrazino[1,2-a]pyrimidines, and 2,3,4,5,6,7-hexahydro-1H-pyrrolo[2,1-c]-[1,4,7]triazacycloundecin-8(9H)-one.     

Five-membered 2,3-Dioxoheterocycles: LIX. Reaction of 3-Aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones with Acyclic β-Enaminoesters. Crystal and Molecular Structure of Ethyl 3-Benzoyl-4-hydroxy-1-o-hydroxyphenyl-5-oxo-2,3-dihydro-1H-pyrrolo-2-spiro-3′-(5-methyl-2-oxo-2,3-dihydro-1H-pyrrolo-4-carboxylate)

3-Aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones react with substituted alkyl 3-amino-2-propenoates to form substituted alkyl 3-aroyl-4-hydroxy-1-o-hydroxyphenyl-5-oxo-2,5-dihydro-1H-pyrrole-2-spiro-3′-(2-oxo-2,3-dihydro-1H-pyrrole-4-carboxylates). Crystal and molecular structure of ethyl 3-benzoyl-4-hydroxy-1-o-hydroxyphenyl-5-oxo-2,5-dihydro-1H-pyrrole-2-spiro-3′-(5-methyl-2-oxo-2,3-dihydro-1H-pyrrole-4-carboxylate) was investigated.     

Pyirolothieno[1,4]diazepines. Part IV. First synthesis of pyrrolo-[1,2-a]thieno[2,3-f][1,4]diazepine Derivatives

Treatment of 3-(2-formyl-1H-pyrrol-1-yl)-2-thiophenecarboxamide by various nucleophiles like methyl ketones, amines, alcohols, thiols or acetates led to new 5,6-dihydro-4H-pyrrolo[1,2-a]thieno-[2,3-f][1,4]diazepines.     

Synthesis of 7H-tetrazolo[1,5-c]pyrrolo[3,2-e]pyrimidines and their reductive ring cleavage to 4-aminopyrrolo[2,3-d]pyrimidines

Some new 7,9-disubstituted 7H-1,2,3,4-tetrazolo[1,5-c]pyrrolo[3,2-e]pyrimidines 5 have been synthesized either by diazotization of 4-hydrazino-5,7-disubstituted-7H-pyrrolo[2,3-d]pyrimidines 4 obtained by hydrazinolysis of 4-chloro-5,7-disubstituted-7H-pyrrolo[2,3-d]pyrimidines 3 or via a substitution reaction between 3 and sodium azide. 5,7-Disubstituted-7H-pyrrolo[2,3-d]pyrimidin-4(3H)-ones 2 were obtained by cyclocondensation of 2-amino-3-cyano-1,4-disubstituted pyrroles 1 with formic acid which on chlorination using phosphorus oxychloride afforded 3 . A novel route for the synthesis of 4-amino-5,7-disubstituted-7H-pyrrolo[2,3-d]pyrimidines 6 by the reductive ring cleavage of 5 has been reported.     

2-Acyl(aroyl)-1,1,3,3-tetracyanopropenides: VI. Reaction with hydrogen halides

Reactions of 2-aroyl-1,1,3,3-tetracyanopropenides with hydrogen halides in solvents of low dielectric permittivity result in the formation of 6-amino-2-aroyl-2-halopyridine-3,5-dicarbonitriles. 2-Acyl-1,1,3,3-tetracyanopropenides under similar conditions afford 2-(2-alkylidene-5-amino-4-cyano-2,3-dihydrofuran-3-ylidene)propanedinitriles. In solvents of high dielectric permittivity the result of the reaction depends on the nature of the hydrogen halide and the acyl(aroyl) substituent: With HCl and HBr 2-aroyl-1,1,3,3-tetracyanopropenides form 2-(5-amino-2-aryl-2-halo-4-cyano-2,3-dihydrofuran-3-ylidene)-propanedinitriles, and 2-acyl-1,1,3,3-tetracyanopropenides give 2-(2-alkylidene-5-amino-4-cyano-2,3-dihydrofuran-3-ylidene)propanedinitriles; with HI depending on the reaction conditions and the structure of the acyl substituent 2-(5-amino-2-aryl-4-cyano-2,3-dihydrofuran-3-ylidene)propanedinitriles, 2-(5-amino-4-cyano-2,3-dihydrofuran-3-ylidene) propane-dinitrile, 2-amino-4-(dimethoxybenzyl)-6-iodo-5-cyanonicotinamide, 4-amino-6-iodo-3-oxo-2,3-dihydro-1H-pyrrolo[3,4-c]pyridine-7-carbonitrile, or 4-amino-6-iodo-3-oxo-1-ethylidene-1,3-dihydrofuro[3,4-c]pyridine-7-carbonitrile are obtained.     

Novel annulated products from aminonaphthyridinones

2-(4-Methoxyphenyl)-1-oxo-1,2-dihydro-1,6-naphthyridine-4-carboxamide (4c) underwent Hofmann rearrangement with iodobenzene diacetate in methanol to give the corresponding 4-amino compound (6c). This, when reacted with 2,4-pentanedione and then hot phosphoryl chloride (attempted Combes synthesis) gave a new heterocyclic system, 6-(4-methoxyphenyl)-2-methylpyrido[3,2-c]pyrrolo[2,3-e]azocin-7(6H)-one (9c). This showed typical pyrrole-type reactivity at the 3-position. Alternatively, an attempt to convert the 4-NH₂ in 6c to 4-OH by diazotization gave, instead, a [1,2,3]triazolo[1,5-a]pyridine-3-carboxaldehyde (16c). The same series of reactions on a benzo analog, 2-methyl-1-oxo-1,2-dihydrobenzo[b][1,6]naphthyridine-4-carboxamide (4a), gave the same results.     

Synthesis of pyrrolo[2,3-c]2,7-naphthyridine derivatives by cascade heterocyclization reaction of 2-amino-4-cyanomethyl-6-dialkylamino-3,5-pyridinedicarbonitriles

Alkylation of the title pyridinedicarbonitriles with N-substituted chloroacetamides was found to give 5,6-diamino-8-dialkylamino-2,3-dihydro-2-oxo-1H-pyrrolo[2,3-c]2,7-naphthyridine-9-carbonitriles. The structure of obtained compounds was unambiguously confirmed by X-ray crystallographic study. The heterocyclization reaction proceeded regioselectively involving 3-CN group of the starting pyridines without participation of 5-CN. The reasons of the selectivity were discussed. An interaction of prepared naphthyridine derivatives with acetic acid anhydride and cyclohexanone yielded 2-dialkylamino-6,8,9,10-tetrahydro-5-methyl-9-oxopyrimido[4,5,6-ij]pyrrolo[2,3-c]2,7-naphthyridine-1-carbonitriles and 2-dialkylamino-4,5,6,8,9,10-hexahydro-9-oxospiro{pyrimido[4,5,6-ij]pyrrolo[2,3-c]2,7-naphthyridine-5,1′-cyclohexane}-1-carbonitriles, respectively. All fused 2,7-naphthyridines obtained were derivatives of novel heterocyclic systems.     

The acid-mediated intramolecular 1,3-dipolar cycloaddition of derived 2-nitro-1,1-ethenediamines for the synthesis of novel fused bicyclic isoxazoles

The discovery of a novel synthesis of new fused bicyclic isoxazoles, for example, N-methyl-3-phenyl-5,6-dihydro-4H-isoxazolo[3,4-c]azepin-8-amine (2a), N-methyl-3-phenyl-4,5-dihydroisoxazolo[3,4-c]pyridin-7-amine (2b) and N-methyl-3-phenyl-4H-pyrrolo[3,4-c]isoxazol-6-amine (2d) in high yield is reported. We speculate that the reaction proceeds via acid-mediated intramolecular 1,3-dipolar cycloaddition from 2-nitro-1,1-ethenediamines 1a,b,d.     

A Novel Approach to the Synthesis of [1,2-a]Fused Polymethylenebenzimidazoles

Abstract

The synthesis of 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazoles and 7,8,9,10-tetrahydro-6H-azepino[1,2-a]benzimidazoles from cyclic amidines is described.