Applying density functional theory on tautomerism in 3,4-dihydropyrimidin-2(1H)-ones

In the present study, the density functional theory (DFT) and Gibbs free energy calculations were performed to investigate the stability and tautomerism of C4-substituted-3,4-dihydropyrimidin-2(1H)-ones. Three different forms are possible for the ethyl 3,4-dihydropyrimidinones (ethyl 4-aryl-6-methyl-3,4-dihydropyrimidin-2(1H)-one-5-carboxylates, ethyl 4-aryl-2-hydroxy-6-methyl-1,4-dihydropyrimidine-5-carboxylates and ethyl 4-aryl-2-hydroxy-6-methyl-3,4-dihydropyrimidine-5-carboxylates) forms that the most stable form is ethyl 4-aryl-6-methyl-3,4-dihydropyrimidin-2 (1H)-one-5-carboxylates (keto-form). The obtained data showed that the substitution on the C4-substitut position can be effective on the equilibrium constant (K _eq).     

3,4-Dimethoxyfuran: Eigenschaften,Berechnungen und Substitutionsreaktionen

3,4-Dimethoxyfuran: Properties, Calculations and some Substitution Reactions 3,4-Dimethoxyfuran (3,4-DF) is much more reactive than furan itself. We present experimental details for the synthesis of this useful compound in 50–100 g batches. 3-4-Dibenzyloxyfuran has also been prepared. Quantum mechanical calculations by PPP-and CNDO-methods analogous to furan itself gave the following information (compared with furan): enhanced negative partial charge at C(2) and C(5), higher acidity at α-position, a stronger and at the same time inverted dipol moment. In accordance with the calculations, 3,4-DF can easily be substituted by weak electrophilic reagents, e.g. in a typical Mannich reaction. The bis-amino compound 8 is produced in good yields. Lithiation by butyl-Li leads to mono- or di-substituted products. The mono- and di-Li-3,4-DF have been used for the preparation of various acylated and alkylated 3,4-DF derivatives. By acid hydrolysis of 3,4-DF crystalline 4-methoxy-3 (2H)-furanone has been prepared.     

Conformational Analysis of 1,2:3,4-Diepoxides: Ab Initio and semiempirical molecular-orbital calculations

Using semiempirical and ab initio procedures, the most stable conformations of meso- and rac-bioxirane and of some substituted 1,2:3,4-diepoxides were calculated. For threo-diepoxides (having the same relative configurations as rac-bioxirane, 3 ), two stable conformations with CCCC dihedral angles of ca. 90 and ca. 270° were found. For erythro-diepoxides (derivatives of meso-bioxirane, 4 ) the calculations suggest three preferred conformations with corresponding dihedral CCCC angles of ca. 90°, ca. 180°, and ca. 270°. The calculations are in fair agreement with the experimental data available for the unsubstituted compounds 3 and 4 .     

Synthesis of pyrido[3,4-b]pyrano[3,4-b]indoles

The synthesis of some pyrido[3,4-b]pyrano[3,4-b]indoles ( 3 ) from 3-hydroxy-4-(3-indolyl)piperidines ( 6 ) is reported.     

Synthesis of pyrano[3,4-c]pyrazole and pyrazolo[3,4-d][1,2]diazepine derivatives

By the action of thionyl chloride on 3(5)-R-4-phenacylpyrazole-5(3)-carboxylic acid ( 3c,d ), 3-R-5-phenylpyrano[3,4-c]pyrazole-7-(1H)ones ( 4c,d ) were obtained. When 4c,d were treated with hydrazine hydrate followed by refluxing in ethanol containing acetic acid, 4,7-dihydro-3-R-5-phenylpyrazolo[3,4-d][1,2]-diazepin-8-(1H)ones ( 6c,d ) were formed. Compounds 6c,d , in turn, were refluxed in ethanol saturated with hydrochloric acid to yield 6-amino-1,6-dihydro-3-R-5-phenyl-7H-pyrazolo[3,4-c]pyridin-7-ones ( 7c,d ). Compounds 7c,d could be obtained directly from 5c,d. The starting materials 3c,d were prepared by hydrolysis of the oxime of 3(5)-R-4-phenacyl-5(3)carboalcoxypyrazoles ( 1a,b ). Structural assignments rested on correct elemental analysis, molecular weights determined by mass spectrometry, and spectroscopic evidence.     

A convenient synthesis of novel pyridazino[3,4-b]quinoxaline and pyrazolo[3,4-b]quinoxaline utilizing 1,3-dipolar cycloaddition reaction

The reaction of 2,6-dichloroquinoxaline 4-oxide 4 with methylhydrazine gave 6-chloro-2-(1-methylhydrazino)quinoxaline 4-oxide 5, whose reaction with dimethyl acetylenedicarboxylate or 2-chloroacrylonitrile resulted in the 1,3-dipolar cycloaddition reaction to afford 7-chloro-3,4-bismethoxycarbonyl-1-methyl-1,2-dihydropyridazino[3,4-b]quinoxaline 6 or 6-chloro-3-hydroxymethylene-1-methyl-2,3-dihydro-1H-pyrazolo[3,4-b] quinoxaline hydrochloride 7, respectively.     

4-phenyl-4H-pyrazolo[3,4-c] furazans. The reactions of 3,4-dacylfuroxans with phenylhydrazine and with aniline

Three different 3,4-diaeylfuroxans (1) are shown to give 3-substituted-l-phenyl-4,5-dioximino-2-pyrazolines (2) upon reaction with phenylhydrazine. The compounds 2 were dehydrated to 6-sul)stituted-4-phenyl-4H-pyrazolo[3,4-c]furazans. ( 3 ) and thermally converted to 3-substituted 5-imino-4-oximino-1-phenyl-2-pyrazolines ( 6 ). The compounds 1 react with aniline to give 3-anilino-4-acylfurazans ( 10 ).     

Synthesis of pyridazino[3,4-b]quinoxalines and pyrazolo[3,4-b]-quinoxaline by 1,3-dipolar cycloaddition reaction

The pyridazino[3,4-b]quinoxalines 6a,b and pyrazolo[3,4-b]quinoxaline hydrochloride 9 were synthesized by the 1,3-dipolar cycloaddition reaction of 6-chloro-2-(1-methylhydrazino)quinoxaline 4-oxide 5 with dimethyl or diethyl acetylenedicarboxylate and 2-chloroacrylonitrile, respectively. The reaction mechanisms were postulated for the formation of 6a,b and 9 .     

Pyrazolo[3,4-b]pyridines. I. Xanthine and isoguanine analogs derived from 1-methylpyrazolo[3,4-b]pyridine

The synthesis of 4,6-dihydroxy-l-methylpyrazolo[3,4-b Jpyridine ( 2 ) and 4-amino-6-hydroxy-1-methylpyrazolo[3,4-b] pyridine ( 3 ) as analogs of xanthine and isoguanine has been accomplished from ethyl 5-amino-1-methylpyrazole-4-carboxylate ( 4 ) and 5-amino-1-methylpyrazole-4-carbo-nitrile ( 6 ), respectively.     

Synthesis of 3-aryl-6H-isoxazolo[3,4-d]pyrazolo[3,4-b]pyridines and 3-aryl-6H-isoxazolo[5,4-d]pyrazolo[3,4-b]pyridines

The synthesis and characterization of a number of 3-aryl-6H-isoxazolo[3,4-d]pyrazolo[3,4-b]pyridines and 3-aryl-6H-isoxazolo[5,4-d]pyrazolo[3,4–6]pyridines from common precursors, 5-benzoyl-4-chloro-1H-pyrazolo-[3,4-b]pyridines, has been described. The structures were determined by unambiguous chemical synthesis and by isolation and ¹³C nmr analysis of some key, isolated, intermediates. The ability of these compounds to displace [3H]flunitrazepam from CNS binding sites was also observed.     

High‐Z′ and twinning behavior in 3,4‐dinitrobenzoic acid

The title compound, C₇H₄N₂O₆, (I), crystallizes in P with Z′ = 4, but with no approximate or pseudosymmetry. The crystals were nonmerohedrally twinned, with at least four twin components related to the major moiety by 180° rotations around the real b and c axes, and by 180° rotation around the a* axis. The excessive twinning is not caused by a phase change from an untwinned room‐temperature higher‐symmetry polymorph. The molecules are planar chiral and, owing to the tilt angle of the nitro groups and the position of protonation, there are altogether eight conformers possible. Six of these theoretically possible eight conformers are realized in the solid‐state structure of (I). Packing analysis and force‐field calculations indicate that the largest part of the packing interactions does not originate from the hydrogen‐bonding interactions, as one might initially be tempted to assume; π–π stacking and O_nitro...π interactions between neighboring molecules of (I) seem to be the dominant factor that determines the packing observed in the structure of this nitro‐substituted benzoic acid derivative.     

Azokupplungen an 3,4-Dimethoxyfuran

Diazo coupling of 3,4-dimethoxyfuran with aryl diazonium ions 3,4-Dimethoxyfuran ( 1 ) easily reacts with aryl diazonium chloride in aqueous pyridine in an expected 1, 4-addition reaction. From the isolable primary addition product pyridine is displaced by alcohols, phenols or thiols to yield 4-alkoxy- or 4-phenoxy- or 4-thiophenoxy-derivatives of 2,3-dimethoxy-2-buten-4-olide ( 3 ). Attempts to convert them into azo compounds by a base catalysed 1, 6-elimination reaction failed. Oxidation of 3a and 3c with DDQ results in the formation of the mono p-nitrophenylhydrazone of 3, 4-dimethoxymaleic acid anhydride. On the other hand, the thiophenoxy compound 3g is smoothly converted by MnO₂ into the authentic furan-2-azobenzene derivative 5 .     

4,5-Dihydropyrazolo[3,4-f]quinazolines

By reaction of 6-dimethylamino-5-oxo-2-phenyl-5,6,7,8-tetrahydroquinazoline with hydrazine, phenylhydrazine, 4-bromo-, 4-chlorophenylhydrazines, and also reaction of 6-dimethylaminomethylene-5-oxo-2-(4-pyridyl)-5,6,7,8-tetrahydroquinazoline with hydrazine, 4-methoxy- and 2-carboxyphenylhydrazines, we have obtained the corresponding 7-phenyl(4-pyridyl)-substituted 1H(2H)- or 1-aryl-4,5-dihydropyrazolo[3,4-f]quinazolines. Methylation of 7-phenyl-4,5-dihydro-1(2H)-pyrazolo[3,4-f]quinazoline by methyl iodide led to its 2-methyl derivative.     

Synthesis,X-Ray Crystal Structure,and Computational Study of Novel Pyrazolo[3,4-B]pyridin-3-Ol Derivatives

Abstract

6-(Pyrazol-1-yl)pyrazolo[3,4-b]pyridin-3-ol (3a) was synthesized by cyclization reaction from 2,6-dichloro-4-methylnicotinonitrile. The related sulfonyl and acylated product (4–7) were obtained from the compound 3a and different sulfonyl and acyl chloride compounds. The sulfonylation of the compound 3a afforded the O1-sulfonylation, only, to give 3-substituted products 4–6. The acylation of the compound 3a gives 1,3-diacylated products 7 via N2, O1-diacylation. All compounds were characterized by spectroscopic methods and the molecular structures of 3a and 4–7 were determined by X-ray diffraction analysis. The molecular structure of 5 and 7 were studied by density functional theory (DFT) calculations, reproduced the experimental geometry. The energies of the three molecules of the tautomeric forms of the compound 3a were calculated by DFT calculations. It was shown that the 3a predominated in the gas phase. Besides, molecular electrostatic potential (MESP) and frontier molecular orbital (FMO) analysis of the compound 3a were investigated by theoretical calculations.

[Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental files: Additional text, tables, and figures.]     

Synthesis of Substituted Pyrrolo[3,4‐a]carbazoles

The cycloaddition between N‐protected 3‐{1‐[(trimethylsilyl)oxy]ethenyl}‐1H‐indoles and substituted maleimides (= 1H‐pyrrole‐2,5‐diones) yielded substituted pyrrolo[3,4‐a]carbazole derivatives bearing an additional succinimide (= pyrrolidine‐2,5‐dione) moiety either at C(5a) or C(10b) depending on the type of the protection group at the indole N‐atom. Derivatives substituted at C(10b) were isolated when the protection group, Me₃Si or Boc (^tBuOCO), was eliminated during the reaction (Schemes 2 and 3), whereas a substitution at C(5a) was observed when an electron‐withdrawing group, Tos (4‐MeC₆H₄SO₂) or pivaloyl (Me₃CCO), was not eliminated (Scheme 1). Complex results were found in reactions between 1‐(trimethylsilyl)‐3‐{1‐[(trimethylsilyl)oxy]ethenyl}‐1H‐indole, in contrast to formerly reported results (Scheme 3). Some derivatives of 1H,5H‐[1,2,4]triazolo[1′,2 : 1,2]pyridazino[3,4‐b]indole‐1,3(2H)‐dione were obtained from reactions with 4‐phenyl‐3H‐1,2,4‐triazole‐3,5(4H)‐dione (Scheme 2). All structures were established by spectroscopic data, by calculations, and one representative structure was confirmed by an X‐ray crystallographic analysis (Fig.). Finally, the formation of the different structure types was discussed, and compared with similar reactions reported in the literature.     

Cycloadditionen von 3,4-Dimethoxyfuran an Benzochinone

Cycloadditions of 3,4-dimethoxyfuran with benzoquinones Cycloaddition of 3,4-dimethoxyfuran (3,4-DF, 1 ) with 1,4-benzoquinones furnishes isolable (2 + 4)-adducts in high yield. The crystalline products with benzoquinone, 2-methyl-benzoquinone, 2,3-dimethoxy-benzoquinone have endo-configuration, whereas 2,3-dimethyl-benzoquinone gives the exo-adduct 4c exclusively. Halogens (Cl₂, Br₂) add rapidly across the highly nucleophilic double bond of 3 or 4 in stereospecific cis-manner, and exclusively from the exo-side. The product 5c shows no sign of enolization to the hydroquinone; but with 3a and 3d the hydroquinones 6 were found. Methanolysis of 5 leads to the stable acetals 7 and 8 . On oxidation of the hydroquinones 7 the thermolabile quinones 10 were obtained. Preparative pyrolysis of 10a under relatively mild conditions (N₂, 200°, 0.1 Torr) gives tetramethoxy ethene ( 11 ) and isobenzofuran-4,7-quinone 12 , a yellowish, crystalline and stable compound.     

Triazoles and Fused Triazoles II: Synthesis of Certain Substituted s-Triazoles,s-Triazolo[3,4-b]-1,3,4-Thiadiazoles and s-Triazolo [3,4-b]-1, 3,4-Thiadiazines

The synthesis of a certain series of s-triazoles and fused s-triazoles namely: 3-(3,4-dimethoxyphenyl)-4-arylideneamino-5-mercapto-s-triazoles 3.8 , 3-(3,4-dimethoxyphenyl)-6-substituted-s-triazolo[3,4-b]-1,3,4-thiadiazoles 11-17 , 3-(3,4-dimethoxyphenyl)-6-substituted thio-s-triazolo[3,4-b]-1,3,4-thiadiazoles 19, 20 and 3-(3,4-dimethoxyphenyl)-6-substituted-7H-s-triazolo[3,4-b]-1,3,4-thiadiazines 21, 22 , is described.     

The reaction of benzotriazoles with 3,4-dihydro-4H-pyrane and 2-acetoxymethyl-3,4-dihydro-2H-pyrane

From the reaction of benzotriazoles with 2,3-dihydro-4H-pyrane and 2-acetoxymethyl-3,4-dihydro-2H-pyrane the corresponding 1-(2-tetrahydropyranyl)benzotriazole and cis-and trans-1-(6-acetoxymethyl-2-tetrahydropyranyl)benzotriazole derivatives were obtained. The structures and conformations of these compounds were confirmed by UV and NMR spectra.     

Synthesis of pyrazolo[3,4-d]pyrimidine derivatives using ketene dithioacetals

The cyclization of 5-amino-3-methylthiopyrazole-4-carbonitriles or 4-carboxamides 3a-j , which were prepared by the reaction of ketene dithioacetals 1a,b [1a : bis(methylthiomethylenemalononitrile; 1b : bis(methylthio)methylenecyanoacetamide] with hydrazines (hydrazine hydrate, phenylhydrazine, p-chlorophenylhydrazine, p-nitrophenylhydrazine), with formamide or carbon disulfide proceeded to give the corresponding 4-amino- or 4-hydroxy-3-methylthiopyrazolo[3,4-d]pyrimidines 6a-h in good yields. 3-Aminopyrazolo[3,4-d]pyrimidine derivatives 6i-1 were also obtained by the application of the cyclization reaction of 3,5-diaminopyrazoles with formamide.     

[3,4]-annulated pyrroles 1. Polynuclear heterocyclic systems based on pyrrolo[3,4-d]pyrimidine-2,4-dione

The intramolecular electrophilic substitution in 6-functionalized 1,3-dimethyl-1H-pyrrolo[3,4-d]pyrimidine-2,4(3H,6H)-diones was used for the synthesis of pyrimido[4′,5′:3,4]-pyrrolo[1,2-a]quinoxaline-8,10(7H,9H)-dione, pyrimido[4′,5′:3,4]pyrrolo[2,1-c][1,2,4]benzo-triazine-8,10(7H,9H)-dione, and 2H-pyrimido[4′,5′:3,4]pyrrolo[1,2-a]indole-2,4,11(1H, 3H)-trione derivatives. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2180–2185, December, 2006.