Low-temperature 1H and 13C NMR spectra of N-substituted 1,2,3,4-tetrahydropyrazino[1,2-a]indoles

The temperature-dependent (1)H and (13)C NMR spectra of 2-(2-butynyl)-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indole (4) (as a representative example of 1-9) in CFCl(3) + CD(2)Cl(2) solution are described and discussed. Below 183 K, the hexahydropyrazine ring inversions become slow on the NMR time-scale and 4 exists in principle as two conformational diastereomers. In fact, only one was observed with the N-2 substituent in an equatorial position as shown by a low-temperature NOESY experiment. The energy barrier for conformational interchange was calculated from NMR data to be 8.3 kcal mol(-1) (1 kcal = 4.184 kJ), in agreement with quantum chemical calculations. Unambiguous assignments for all proton and carbon resonances of 1-9 were made using 1D (APT, DEPT, NOE difference) and 2D (COSY, NOESY, gHMQC, gHMBC) NMR techniques.     

Stereoselective synthesis of 4-substituted 1,2,3,4,10,10a-hexahydropyrazino[1,2-<Emphasis Type="Italic">a</Emphasis>]indoles

4-Substituted 1,2,3,4-tetrahydropyrazino[1,2-a]indoles were synthesized from 2-cyanoindole. (R)-4-Methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indole was obtained by the Mitsunobu reaction. Stereoselective reduction of 4-substituted 1,2,3,4-tetrahydropyrazino[1,2-a]indoles gave 4-substituted 1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indoles. (4R, 10aR)-4-Methyl-1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indole was synthesized.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 221–225, January, 2005.     

Synthese von imidazo[1,5-a]- und pyrazino[1,2-a]benzimidazolen

1,2-Dihydro-3H-imidazo[1,5-a]benzimidazoles (6), 1-oxo-1,2-dihydro-3H-imidazo[ 1,5-a] benzimidazoles (8), 3H-imidazo[1,5-a]benzimidazoles (7), 3-oxo-1,2,3,4-tetrahydro-pyrazino[1,2-a] benzimidazoles (12), and 3,4-dioxo-1,2,3,4-tetrahydro-pyrazino[1,2-a]benzinudazoles (13) were synthesized from 2-α-aminobenzyl (benzhydryl)-benzimidazoles (2).     

Novel routes to 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazines and 5,6,9,10,11,11a-hexahydro-8H-pyrido[1,2-a]pyrrolo[2,1-c]pyrazines

Condensation reactions of benzotriazole and 2-(pyrrol-1-yl)-1-ethylamine (1) with formaldehyde and glutaric dialdehyde, respectively, afforded intermediates 2 and 6. Subsequent nucleophilic substitutions of the benzotriazole group in 2 and 6 with Grignard reagents, sodium cyanide, and sodium borohydride gave 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazines 3a-e, 4, 5 and 5,6,9,10,11,11a-hexahydro-8H-pyrido[1,2-a]pyrrolo[2,1-c]pyrazines 7a-c, 8, 9, respectively, in good yields.     

Novel synthesis of benzalacetone analogues of naphth[a]azulenes by intramolecular tropylium ion-mediated furan ring-opening reaction and X-ray investigation of a naphth[1,2-a]azulene derivative

[reaction: see text] Benzalacetone analogues of naphth[1,2-a]azulene (8), naphth[2,1-a]azulene (13), and naphth[2,3-a]azulene (18) were synthesized from 2-(5-methyl-2-furyl)-1-tropylionaphthalene (7), 1-(5-methyl-2-furyl)-2-tropylionaphthalene (12), and 2-(5-methy-2-furyl)-3-tropylionaphthalene (17), respectively. The synthetic method is based on furan ring-opening reaction by the intramolecular electrophilic attack of a tropylium ion. Single-crystal X-ray work on the naphth[1,2-a]azulene derivative (8) revealed that its tetracyclic system exhibited deformation from planarity similar to that of benzo[c]phenanthrene (tetrahelicene). A centrosymmetric associated dimer structure, just like the molecules of carboxylic acids but via C=O...H-C hydrogen bonds, was found in the crystal. Reduction of bond-length alternation in the seven-membered ring was also found.     

Cycloaddition of 2-acylmethyl-1H-benzimidazoles to 4-arylidene-1,3-oxazol-5-ones

Cycloaddition of 2-phenacyl-1H-benzimidazole to 2-phenyl-or 2-methyl-4-arylidene-1,3-oxazol-5-ones occurs regioselectively to form the previously unknown N-(3-aryl-4-benzoyl-1-oxo-1,2,3,4-tetrahydropyrido[1,2-a]benzimidazol-2-yl)benz-and-acetamides. The analogous cycloaddition of the 2-acetonyl-1H-benzimidazole is complicated by prototropic isomerization and leads to the corresponding 1,2,3,5-tetrahydropyrido[1,2-a]benzimidazole. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 78, pp. 1008–1014, July, 2007.     

Unique substituted 3-oxo-1,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole-1-carboxamides generated by Ugi 3CC using bifunctional starting material

2-(2-Formyl-1H-benzimidazol-1-yl)acetic acid, as a bifunctional formyl-acid was prepared in four steps. This compound underwent one-pot reaction with primary amines, and alkyl isocyanides under Ugi conditions. A series of novel 3-oxo-1,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole-1-carboxamides were obtained in moderate to excellent yields.     

Highly efficient one-pot synthesis of 1-substituted-1,2,3,4-tetrahydropyrazino[1,2-a]indoles

A practical and general one-pot synthesis of 1-substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles is described. The approach uses 2-(3-methyl-1H-indol-1-yl) ethylamine, benzotriazole and aldehydes in the presence of catalytic amount of acid catalysts (AlCl₃, ZnCl₂, ZnBr₂, p-TsOH, CH₃SO₃H) and proceeds in high yields via iminium cation intramolecular cyclization. The mechanism of the observed intramolecular cyclization reaction has been investigated theoretically by means of PM3 semiempirical method and results were consistent with the experimental results.     

Polynuclear heterocyclic compounds containing an indole fragment

Derivatives of 6,7,9,10,11,12-hexahydro-5H-indolo[3,2,1-d,e]phenazine and 1,2,3,4-tetrahydroindolo[1,2-a]quinoxaline were obtained by condensation of the sodium derivatives of 1-keto-1,2,3,4-tetrahydrocarbazoles and 2-aroylindoles, respectively, with-bromocyclohexanone dimethylketal. These compounds are converted to derivatives of indolo[1,2-a]-quinoxaline, 5,6-dihydroindolo[1,2-a]quinoxaline, and 8a,9,10,11,12,12a-hexahydro- and 5,6,7,7a,8a,9,10,11,12,12a-decahydro-8H-indolo[3,2,1-d,e]phenazine by dehydrogenation over a Raney nickel catalyst and reduction with sodium in alcohol.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1348–1352, October, 1970.     

Imidazo[1,2-a]pyridines. I. Synthesis and inotropic activity of new 5-imidazo[1,2-a]pyridinyl-2(1H)-pyridinone derivatives

A series of 1,2-dihydro-5-imidazo[1,2-a]pyridinyl-2(1H)-pyridonones was synthesized and evaluated for positive inotropic activity, 1,2-Dihydro-5-imidazo[1,2-a]pyridin-6-yl-6-methyl-2- oxo-3-pyridinecarbonitrile (11a) hydrochloride monohydrate (E-1020) was found to be a potent and selective inhibitor of phosphodiesterase III and a long-acting, potent, orally active positive inotropic agent. Additional imidazo[1,2-a]pyridin-2-yl (3a), -3-yl (16), -7-yl (20) and -8-yl (24a) compounds were also prepared. Altering the pyridine substitution from the 2-position to the 6-position produced a 2-fold increase in the i.v. cardiotonic potency (ED50) from 52 to 23 micrograms/kg, while substitution at the 3-, 7- or 8-position reduced potency. In the 2-positional isomers, introduction of halogen groups enhanced the activity and 3-chloro-1,2-dihydro-5-(6-fluoroimidazo[1,2-a] pyridin-2-yl)-6-methyl-2(1H)-pyridinone (3u) was the most potent (i.v. ED50 11 micrograms/kg) in this series. E-1020 is presently under development for the treatment of congestive heart failure.     

A novel synthesis of arylpyrrolo[1,2-a]pyrazinone derivatives

Some aryl-2-methyl-1-pyrrolo[1,2-a]pyrazinones were designed and prepared to study the Structure-Activity Relationships (SAR) of pyrrolo[1,2-a]pyrazinone derivatives. With methyl pyrrole-2-carboxylate as the starting material, the title compounds were prepared through N-alkylation and two novel cyclizations. Eleven aryl-2-methyl-1- pyrrolo[1,2-a]pyrazinone derivatives not previously reported in the literature are presented in this paper. Some of them show potent anti-inflammatory and analgesic activities.     

Chemistry of acyl(imidoyl)ketenes. 8*. Thermolysis of 3-alkoxycarbonyl- 5-phenyl-1,2,4,5-tetrahydropyrrolo[1,2-a]- quinoxaline-1,2,4-triones. Structure of 2-(3-oxo-4-phenyl-3,4-dihydro-2-quinoxalinyl)- 2,4-di(ethoxycarbonyl)-6-phenyl-2,3,5,6-tetrahydro- 1h-pyrido[1,2-a]quinoxaline-1,3,5-trione

3-Alkoxycarbonylmethylene-1-phenyl-1,2,3,4-tetrahydro-2-quinoxalones, obtained by the interaction of dialkyl esters of oxaloacetic acid and N-phenyl-o-phenylenediamine, react with oxalyl chloride with the formation of 3-alkoxycarbonyl-5-phenyl-1,2,4,5-tetrahydropyrrolo[1,2-a]quinoxaline-1,2,4-triones. Alkoxycarbonyl(2-oxo-1-phenyl-1,2-dihydro-3-quinoxalinyl)ketenes, generated on thermal decarbonylation of the latter, are stabilized by participation in a [4+2] cyclodimerization reaction with the formation of 2,4-di(alkoxycarbonyl)-2-(3-oxo-4-phenyl-3,4-dihydro-2-quinoxalinyl)-6-phenyl-2,3,5,6-tetrahydro-1H-pyrido[1,2-a]quinoxaline-1,3,5-triones. The crystal and molecular structure of the di(ethoxycarbonyl) derivative have been investigated by X-ray structural analysis.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1501–1506, October, 2004.     

Reaction of 2,3,3-trimethyl-3H-indole hydrochloride with methacrylic and crotonic amides

Reaction of 2,3,3-trimethyl-and 2,3,3,5-tetramethyl-3H-indole hydrochlorides with methacrylic and crotonic amides gives 3- and 4-methyl-1,2,3,4,10,10a-hexahydropyrimido[1,2-a]indol-2-ones. With perchloric acid these are converted to 1-carbamoylpropyl-3H-indolium perchlorates. The syntheses of 10a-(4-dimethylaminostyryl)- and 10a-[(4-dimethylaminophenyl)butadienyl]-3,10,10-trimethylpyrimido[1,2-a]indol-2-ones have been studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 625–627, May, 1990.     

Investigation of the products of the reaction of epichlorohydrin with aromatic amines

The synthesis of 2-(hydroxymethyl)benz [g]indoline derivatives by heating N-acyl derivatives of 2-(chloromethyl)benz[g]indoline in dimethyl sulfoxide is described. 3,6-Dichloro-1,2,3,4-tetrahydrobenzo[h]quinoline, 5-chloroazirido[1,2-a]benz[g]indoline, and derivatives of 2-substituted 5-chlorobenz [g]indoline were synthesized.See [1] for communication XITranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1111–1116, August, 1972.     

2,3,5,8(1)-Tetrahydroimidazo[1,2-a]pyrimidine-2,5-dione derivatives

The corresponding ylidene, azomethine, and azo derivatives of 2,3,5,8(1)-tetrahydroimidazo [1,2-a]pyrimidine-2,5-dione were synthesized by reaction of 7-methyl-and 6-bromo-7-methyl-2,3,5,8(1)-tetrahydroimidazo[1,2-a]pyrimidine-2,5-diones with aldehydes, insatin, aromatic nitroso compounds, and arenediazonium salts. Ylidene derivatives of 7-methyl-2,3,5,8(1)-tetrahydroimidazo[1,2-a]pyrimidine-2,5-dione were also obtained by reaction of 2-amino-4-methyl-6-oxo-1,6-dihydro-1-pyrimidylacetic acid with carbonyl compounds.     

Thermal and hydrolytic decomposition of derivatives of N-(1-Piperidinoanthra-quinon-2-yl)oxaziridine

On being heated in toluene or treated with alcoholic alkalies, 3-phenyl- and 3-methyl-2-(1-piperidinoanthraquinon-2-yl) oxaziridines undergo both isomerization into 1-piperidino-2-acylaminoanthraquinones and also conversion into 8, 13-dioxo-1, 2, 3, 4, 8,13-hexahydropyridyl [1,2-a]-anthra [2,1-d]imidazole.     

The Mannich reaction in the synthesis of N,S-containing heterocycles. 7. Effective one-pot synthesis of derivatives of spiro[3,5,7,11-tetraazatricyclo-[7.3.1.0<Superscript>2,7</Superscript>]tridec-2-ene-13,4′-piperidine]

5,11-Disubstituted derivatives of 1′-isopropyl-8-thioxospiro[3,5,7,11-tetrazatricyclo[7.3.1.0^2,7]tridec-2-ene-13,4′-piperidine]-1,9-dicar bonitrile was obtained by the interaction of 10-amino-9-aza-3-azonia-7,11-dicyano-3-isopropylspiro[5,5]undeca-7,10-diene-8-thiolate with 2 equiv. of a primary amine and excess of formaldehyde. An anomalous reaction product was obtained with o-toluidine — 7,9-dicyano-1′-isopropyl-3-(2-methylphenyl)-1,2,3,4-tetrahydrospiro[pyrido[1,2-a][1,3,5]triazine-8,4′-piper idinium]-6-thiolate. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, 1709–1713, November, 2007.     

Investigation of naphthyridines. VII. Synthesis of 10-alkylamino-1,2,3,4-tetrahydrobenzo[b]-1,6-naphthyridines

10-Alkylamino-2-methy1-1,2,3,4-tetrahydrobenzo[b]-1,6-naphthyridines were obtained by cyclization of alkylamides of N-(1-methyl-4-piperidylidene)anthranilic acids and also by reaction of 10-chloro-2-methyl-1,2,3,4-tetrahydrobenzo-[b]-1,6-naphthyridines with amine hydrochlorides.See [1] for communication VI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 263–265, February, 1976.     

The reaction of 2-hetarylacetonitriles with heterocyclic haloaldehydes

The reaction of 4-oxo-3,4-dihydroquinazolyl-and benzimidazolylacetonitriles with 2-chloro-2-quinolinecarbaldehydes and 1-aryl-5-chloro-3-methyl-1H-pyrazole-4-carbaldehydes gave the corresponding 3-(2-chloro-3-quinolyl)-2-(4-oxo-3,4-dihydro-2-quinazolyl)-2-propenenitriles and 3-(1-aryl-5-chloro-3-methyl-1H-4-pyrazolyl)-2-hetaryl-2-propenenitriles. Intramolecular cyclization of these compounds gives 15-oxo-15H-benzo[6,7][1,8]naphthyridino[2,1-b]quinazoline-6-carbonitriles, 1-aryl-3-methyl-11-oxo-1,11-dihydropyrazolo[4′,3′:5,6]pyrido[2,1-b]quinazoline-5-carbonitriles, and 1-aryl-3-methyl-1H-benzo[4,5]imidazo[1,2-a]pyrazolo[4,3-e]pyridine-5-carbonitriles.     

Synthesis and conversions of 3-(4-amino-5-methyl-4H-1,2,4-triazol-3-ylmethylene)-2-oxo-1,2,3,4-tetrahydroquinoxaline

The reaction of the hydrazone 3a with hydrazine hydrate in DBU/ethanol conveniently gave 3-(4-amino-5-methyl-4H-1,2,4-triazol-3-ylmethylene)-2-oxo-1,2,3,4-tetrahydroquinoxaline 6 . The reactions of 6 with an equimolar and 2-fold molar amount of nitrous acid afforded 3-(α-hydroxyimino-4-amino-5-methyl-4H-1,2,4-triazol-3-ylmethyl)-2-oxo-1,2-dihydroquinoxaline 9 and 3-(α-hydroxyimino-5-methyl-2H-1,2,4-triazol-3-ylmethyl)-2-oxo-1,2-dihydroquinoxaline 10 , respectively, which were converted into the 3-heteroarylisoxazolo[4,5-b]quin-oxalines 13a,b and 11 , respectively. Compound 9 was also cyclized into the 8-quinoxalinyl-1,2,4-triazolo-[3,4-f][1,2,4]triazines 14a,b .