Facile Route to Novel Pyrazolo[3,4‐d]pyrimidine,Imidazo[1,2‐b] pyrazole,Pyrazolo[3,4‐d][1,2,3]triazine,Pyrazolo[1,5‐c][1,3,5]triazine and Pyrazolo[1,5‐c][1,3,5]thiadiazine Derivatives

A regioselective synthesis of novel pyrazolo[3,4‐d]pyrimidines, imidazo[1,2‐b]pyrazoles, pyrazolo[3,4‐d][1,2,3]triazine, pyrazolo[1,5‐c][1,3,5]triazine and pyrazolo[1,5‐c][1,3,5]thiadiazine incorporating a thiazole moiety was described via the reactions of the versatile, readily accessible 5‐amino‐3‐(phenylamino)‐N‐(4‐phenylthiazol‐2‐yl)‐1H‐pyrazole‐4‐carboxamide ( 1 ) with each of DMF‐DMA, phenylisothiocyanate, chloroacetyl chloride, phenacyl bromide, benzoylisothiocyanate and formalin, respectively. All structures of the newly synthesized compounds were elucidated by elemental analysis and spectral data.     

2‐Ethylsulfanyl‐7‐(furan‐2‐yl)‐4‐(thiophen‐2‐yl)pyrazolo[1,5‐a][1,3,5]triazine: π‐stacked chains of hydrogen‐bonded R22(10) dimers

In the title compound, C₁₅H₁₂N₄OS₂, the bond distances in the fused heterocyclic system show evidence for aromatic‐type delocalization in the pyrazole ring with some bond fixation in the triazine ring. The thiophenyl substituent is slightly disordered over two sets of atomic sites having occupancies of 0.934 (4) and 0.066 (4). The non‐H atoms in the entire molecule are nearly coplanar, with the planes of the furanyl substituent and the major orientation of the thiophenyl substituent making dihedral angles of 5.72 (17) and 1.8 (3)°, respectively, with that of the fused ring system. Molecules are linked into centrosymmetric R₂²(10) dimers by C—H...O hydrogen bonds and these dimers are further linked into chains by a single π–π stacking interaction. Comparisons are made with some related 4,7‐diaryl‐2‐(ethylsulfanyl)pyrazolo[1,5‐a][1,3,5]triazines which contain variously substituted aryl groups in place of the furanyl and thiophenyl substituents in the title compound.     

Conversion of 3‐amino‐4‐arylamino‐1H‐isochromen‐1‐ones to 1‐arylisochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐ones: synthesis,spectroscopic characterization and the structures of four products and one ring‐opened derivative

An efficient synthesis of 1‐arylisochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐ones, involving the diazotization of 3‐amino‐4‐arylamino‐1H‐isochromen‐1‐ones in weakly acidic solution, has been developed and the spectroscopic characterization and crystal structures of four examples are reported. The molecules of 1‐phenylisochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐one, C₁₅H₉N₃O₂, (I), are linked into sheets by a combination of C—H…N and C—H…O hydrogen bonds, while the structures of 1‐(2‐methylphenyl)isochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐one, C₁₆H₁₁N₃O₂, (II), and 1‐(3‐chlorophenyl)isochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐one, C₁₅H₈ClN₃O₂, (III), each contain just one hydrogen bond which links the molecules into simple chains, which are further linked into sheets by π‐stacking interactions in (II) but not in (III). In the structure of 1‐(4‐chlorophenyl)isochromeno[3,4‐d][1,2,3]triazol‐5(1H)‐one, (IV), isomeric with (III), a combination of C—H…O and C—H…π(arene) hydrogen bonds links the molecules into sheets. When compound (II) was exposed to a strong acid in methanol, quantitative conversion occurred to give the ring‐opened transesterification product methyl 2‐[4‐hydroxy‐1‐(2‐methylphenyl)‐1H‐1,2,3‐triazol‐5‐yl]benzoate, C₁₇H₁₅N₃O₃, (V), where the molecules are linked by paired O—H…O hydrogen bonds to form centrosymmetric dimers.     

Two regioisomers of condensed thioheterocyclic triazine synthesized from 6‐phenyl‐3‐thioxo‐2,3,4,5‐tetrahydro‐1,2,4‐triazin‐5‐one

In the crystal structure of 6‐phenyl‐3‐thioxo‐2,3,4,5‐tetrahydro‐1,2,4‐triazin‐5‐one, C₉H₇N₃OS, (I), the 1,2,4‐triazine moieties are connected by face‐to‐face contacts through two kinds of double hydrogen bonds (N—H...O and N—H...S), which form planar ribbons along the a axis. The ribbons are crosslinked through C—H...π interactions between the phenyl rings. The molecular structures of two regioisomeric compounds, namely 6‐phenyl‐2,3‐dihydro‐7H‐1,3‐thiazolo[3,2‐b][1,2,4]triazin‐7‐one, C₁₁H₉N₃OS, (II), and 3‐phenyl‐6,7‐dihydro‐4H‐1,3‐thiazolo[2,3‐c][1,2,4]triazin‐4‐one, C₁₁H₉N₃OS, (III), which were prepared by the condensation reaction of (I) with 1,2‐dibromoethane, have been characterized by X‐ray crystallography and spectroscopic studies. The crystal structures of (II) and (III) both show two crystallographically independent molecules. While the two compounds are isomers, the unit‐cell parameters and crystal packing are quite different and (II) has a chiral crystal structure.     

Hydrogen‐bonded chains of rings in 1‐(4‐chloroanilinomethyl)‐5‐(4‐chlorophenyl)‐1,3,5‐triazinane‐2‐thione and hydrogen‐bonded sheets in 1‐anilinomethyl‐5‐phenyl‐1,3,5‐triazinane‐2‐thione

In 1‐(4‐chloroanilinomethyl)‐5‐(4‐chlorophenyl)‐1,3,5‐triazinane‐2‐thione, C₁₆H₁₆Cl₂N₄S, there are two independent molecules in the asymmetric unit which form inversion dimers via two weak N—H...S hydrogen bonds. The dimers are then linked into C(9)C(14) chains by a C—H...S hydrogen bond and a C—H...Cl contact. In 1‐(anilinomethyl)‐5‐phenyl‐1,3,5‐triazinane‐2‐thione, C₁₆H₁₈N₄S, molecules are linked into complex sheets via a combination of N—H...S and C—H...π hydrogen bonds.     

Reactions of Imidoyl Isoselenocyanates with Aromatic 2‐Amino N‐Heterocycles and 1‐Methyl‐1H‐imidazole

The reaction of N‐phenylimidoyl isoselenocyanates 1 with 2‐amino‐1,3‐thiazoles 10 in acetone proceeded smoothly at room temperature to give 4H‐1,3‐thiazolo[3,2‐a] [1,3,5]triazine‐4‐selones 13 in fair yields (Scheme 2). Under the same conditions, 1 and 2‐amino‐3‐methylpyridine ( 11 ) underwent an addition reaction, followed by a spontaneous oxidation, to yield the 3H‐4λ⁴‐[1,2,4]selenadiazolo[1′,5′:1,5] [1,2,4]selenadiazolo[2,3‐a]pyridine 14 (Scheme 3). The structure of 14 was established by X‐ray crystallography (Fig. 1). Finally, the reaction of 1‐methyl‐1H‐imidazole ( 12 ) and 1 led to 3‐methyl‐1‐(N‐phenylbenzimidoyl)‐1H‐imidazolium selenocyanates 15 (Scheme 4). In all three cases, an initially formed selenourea derivative is proposed as an intermediate.     

Eth­yl 5‐isoprop­oxy‐4‐meth­yl‐β‐carboline‐3‐carboxyl­ate: structural determinants of benzodiazepine‐receptor antagonism

Mol­ecules of the title compound, C₁₈H₂₀N₂O₃, are linked into ribbons by N—H·O and N—H·N hydrogen bonds. Stereochemical comparison with Ro 15‐1788 (viz. eth­yl 8‐fluoro‐5,6‐dihydro‐5‐meth­yl‐6‐oxo‐4H‐imidazo[1,5‐a][1,4]benzodiazepine‐3‐carboxyl­ate) has identified three electronegative N and O atoms in the mol­ecule as features likely to be responsible for its activity as a benzodiazepine‐receptor antagonist.     

Cocrystals of 2,6‐dichloroaniline and 2,6‐dichlorophenol plus three new pseudopolymorphs of their coformers

The structures of cocrystals of 2,6‐dichlorophenol with 2,4‐diamino‐6‐methyl‐1,3,5‐triazine, C₆H₄Cl₂O·C₄H₇N₅, (III), and 2,6‐dichloroaniline with 2,6‐diaminopyrimidin‐4(3H)‐one and N,N‐dimethylacetamide, C₆H₅Cl₂N·C₄H₆N₄O·C₄H₉NO, (V), plus three new pseudopolymorphs of their coformers, namely 2,4‐diamino‐6‐methyl‐1,3,5‐triazine–N,N‐dimethylacetamide (1/1), C₄H₇N₅·C₄H₉NO, (I), 2,4‐diamino‐6‐methyl‐1,3,5‐triazine–N‐methylpyrrolidin‐2‐one (1/1), C₄H₇N₅·C₅H₉NO, (II), and 6‐aminoisocytosine–N‐methylpyrrolidin‐2‐one (1/1), C₄H₆N₄O·C₅H₉NO, (IV), are reported. Both 2,6‐dichlorophenol and 2,6‐dichloroaniline are capable of forming definite synthon motifs, which usually lead to either two‐ or three‐dimensional crystal‐packing arrangements. Thus, the two isomorphous pseudopolymorphs of 2,4‐diamino‐6‐methyl‐1,3,5‐triazine, i.e. (I) and (II), form a three‐dimensional network, while the N‐methylpyrrolidin‐2‐one solvate of 6‐aminoisocytosine, i.e. (IV), displays two‐dimensional layers. On the basis of these results, attempts to cocrystallize 2,6‐dichlorophenol with 2,4‐diamino‐6‐methyl‐1,3,5‐triazine, (III), and 2,6‐dichloroaniline with 6‐aminoisocytosine, (V), yielded two‐dimensional networks, whereby in cocrystal (III) the overall structure is a consequence of the interaction between the two compounds. By comparison, cocrystal–solvate (V) is mainly built by 6‐aminoisocytosine forming layers, with 2,6‐dichloroaniline and the solvent molecules arranged between the layers.     

Different patterns of supramolecular assembly in constitutionally similar 6‐arylimidazo[2,1‐b][1,3,4]thiadiazoles

Four imidazo[2,1‐b][1,3,4]thiadiazoles containing a simply‐substituted 6‐aryl group have been synthesized by reaction of 2‐amino‐1,3,4‐thiadiazoles with bromoacetylarenes using microwave irradiation and brief reaction times. 6‐(2‐Chlorophenyl)imidazo[2,1‐b][1,3,4]thiadiazole, C₁₀H₆ClN₃S, (I), 6‐(2‐chlorophenyl)‐2‐methylimidazo[2,1‐b][1,3,4]thiadiazole, C₁₁H₈ClN₃S, (II), 6‐(3,4‐dichlorophenyl)imidazo[2,1‐b][1,3,4]thiadiazole, C₁₀H₅Cl₂N₃S, (III), and 6‐(4‐fluoro‐3‐methoxyphenyl)‐2‐methylimidazo[2,1‐b][1,3,4]thiadiazole, C₁₂H₁₀FN₃OS, (IV), crystallize with Z′ values of 2, 1, 1 and 2 respectively. The molecular skeletons are all nearly planar and the dihedral angles between the imidazole and aryl rings are 1.51 (8) and 7.28 (8)° in (I), 9.65 (7)° in (II), 10.44 (8)° in (III), and 1.05 (8) and 7.21 (8)° in (IV). The molecules in (I) are linked by three independent C—H...N hydrogen bonds to form ribbons containing alternating R₂²(8) and R₄⁴(18) rings, and these ribbons are linked into a three‐dimensional array by three independent π‐stacking interactions. Both (II) and (III) contain centrosymmetric dimers formed by π‐stacking interactions but hydrogen bonds are absent, and the molecules of (IV) are linked into centrosymmetric R₂²(8) dimers by C—H...N hydrogen bonds. Comparisons are made with a number of related compounds.     

Synthesis of nitrogen‐containing heterocycles 9. Preparation and carbon‐carbon bond cleavage of spiro[cycloalkane[1′,2′,4′]‐triazolo[1′,5′‐a][1′,3′,5′]triazine] derivatives and related compounds

Diaminomethylenehydrazones of cyclic ketones 1–5 reacted with ethyl N‐cyanoimidate (I) at room temperature or with bis(methylthio)methylenecyanamide (II) under brief heating to give directly the corresponding spiro[cycloalkane[1′,2′,4′]triazolo[1′,5′,‐a][1′,3′‐5′]triazine] derivatives 7–12 in moderate to high yields. Ring‐opening reaction of the spiro[cycloalkanetriazolotriazine] derivatives occurred at the cycloalkane moiety upon heating in solution to give 2‐alkyl‐5‐amino[1,2,4]triazolotriazines 13–16. Diaminomethylenehydrazones 17–19, of hindered acyclic ketones, gave 2‐methyl‐7‐methylthio[1,2,4]‐triazolo[1,5‐a][1,3,5]triazines 21–23 by the reaction with II as the main products with apparent loss of 2‐methylpropane from the potential precursor, 2‐tert‐butyl‐2‐methyl‐7‐methylthio[1,2,4]triazolo[1,5‐a]‐[1,3,5]triazines 20, in good yields. In general, bis(methylthio)methylenecyanamide II was found to be a favorable reagent to the one‐step synthesis of the spiro[cycloalkanetriazolotriazine] derivatives from the diaminomethylenehydrazones. The spectral data and structural assignments of the fused triazine products are discussed.     

2‐[N‐(X‐Chlorophenyl)carbamoyl]benzenesulfonamide (with X = 2 and 4)

The structures of 2‐[N‐(2‐chlorophenyl)carbamoyl]benzenesulfonamide and 2‐[N‐(4‐chlorophenyl)carbamoyl]benzenesulfonamide, both C₁₃H₁₁ClN₂O₃S, are stabilized by extensive intra‐ and intermolecular hydrogen bonds. In both structures, sulfonamide groups are hydrogen bonded via the N and O atoms and form chains of molecules. The carbamoyl groups are also hydrogen bonded, involving the O and N atoms, further strengthening the polymeric chains running along the c and a axes in the 2‐ and 4‐chloro derivatives, respectively. Carbamoylsulfonamide derivatives are novel compounds with a great potential for medicinal applications.     

Interaction of 4‐Oxo‐4H‐pyrazolo[5,1‐c][1,2,4]triazin‐1‐ides with Grignard Reagents

Reactions of magnesium 3‐tert‐butyl‐8‐R‐4‐oxo‐4H‐pyrazolo[5,1‐c][1,2,4]triazin‐1‐ides (R = CN, CO₂Et) with AlkMgBr led to nucleophilic additions to either side chain or triazine core, with selectivity being dependent on the nature of substituents, as well as on the solvents used. Previously inaccessible C⁸‐functionalized and C⁴‐functionalized pyrazolo[5,1‐c][1,2,4]triazines and 3‐tert‐butyl‐3‐ethyl‐4‐oxo‐1,2,3,4‐tetrahydropyrazolo[5,1‐c][1,2,4]triazine were synthesized, and their reactivity and spectral data discussed.     

Study of the Reaction of 5‐Aryl‐7‐hydrazino‐2‐phenylpyra‐zolo[1,5‐c]pyrimidines with 1,3‐Dicarbonyl Compounds

A novel synthetic method for the preparation of 5‐aryl‐7‐(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐2‐phenylpyrazolo[1,5‐c]‐pyrimidines and 1‐(5‐aryl‐2‐phenylpyrazolo[1,5‐c]pyrimidin‐7‐yl)‐3‐methyl‐1H‐pyrazol‐5‐ols is provided by condensative cyclization of 5‐aryl‐7‐hydrazino‐2‐phenylpyrazolo[1,5‐c]pyrimidines with 1,3‐dicarbonyl compounds. The study of the more reactive position for electrophilic substitusion reactions on such ring system was also achieved.     

Researches on thiazolobenzodiazepines: Behavior of tetrahydro‐1,5‐benzodiazepinethiones with aromatic α‐haloketones

A number of 1‐substituted 4H,5H,6H‐[1,3]thiazolo[3,2‐a][1,5]benzodiazepinium‐11‐bromides and S‐(2‐oxo‐2‐phenyl‐X‐(p)‐ethyl)‐3‐(2‐methyl‐1H‐benzimidazol‐1‐yl) propane (or butane) thioate hydrobromides were obtained by direct reaction of the 5‐acetyl(or formyl, or anilinocarbonyl)‐substituted tetrahydro‐1,5‐benzodiazepine‐2‐thiones with aromatic α‐bromoketones. 2‐[(1‐Acetyl‐2(or 3)‐methyl‐2,3‐dihydro‐1H‐1,5‐benzodiazepin‐4‐yl) sulfanyl]‐1‐phenylethanones as intermediates of the formation of thiazolo [3,2‐a][1,5]benzodiazepine and N‐substituted 2‐methyl‐1H‐benzimidazole derivatives have been synthesized. Semiempirical AM1 calculations of a mechanism and energetic parameters for the heptatomic nucleus rearrangement to benzimidazole ring are presented. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:72–81, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20414     

The molecular and supramolecular structures of four 1,5,6,10b‐tetrahydropyrazolo[1,5‐c]quinazolines

The supramolecular structures of the title compounds, 2‐phenyl‐5‐p‐tolyl‐1,5,6,10b‐tetra­hydro­pyrazolo­[1,5‐c]quinazoline, C₂₃H₂₁N₃, (I), 5‐(4‐bromo­phenyl)‐2‐phenyl‐1,5,6,10b‐tetra­hydro­pyrazolo­[1,5‐c]­quinazoline, C₂₂H₁₈BrN₃, (II), 2‐(4‐chlorophenyl)‐5‐phenyl‐1,5,6,10b‐tetrahydropyrazolo[1,5‐c]quinazoline, C₂₂H₁₈ClN₃, (III), and 5‐(4‐bromo­phenyl)‐2‐(4‐chlorophenyl)‐1,5,6,10b‐tetrahydropyrazolo[1,5‐c]quinazoline, C₂₂H₁₇BrClN₃, (IV), are of two general types. Compounds (I), (II) and (III) form base‐paired dimers via N—H?N hydrogen bonds, where (I) and (II) are isomorphous, while in (IV), there are no conventional hydrogen bonds.     

A chain of π‐stacked molecules in 4‐(2‐chlorophenyl)pyrrolo[1,2‐a]quinoxaline and a hydrogen‐bonded sheet in (4RS)‐4‐(1,3‐1,3‐benzodioxol‐6‐yl)‐4,5‐dihydropyrrolo[1,2‐a]quinoxaline

In the molecule of 4‐(2‐chlorophenyl)pyrrolo[1,2‐a]quinoxaline, C₁₇H₁₁ClN₂, (I), the bond lengths are consistent with electron delocalization in the two outer rings of the fused tricyclic system, with a localized double bond in the central ring. The molecules of (I) are linked into chains by a π–π stacking interaction. In (4RS)‐4‐(1,3‐benzodioxol‐6‐yl)‐4,5‐dihydropyrrolo[1,2‐a]quinoxaline, C₁₈H₁₄N₂O₂, (II), the central ring of the fused tricyclic system adopts a conformation intermediate between screw‐boat and half‐chair forms. A combination of N—H...O and C—H...π(arene) hydrogen bonds links the molecules of (II) into a sheet. Comparisons are made with related compounds.     

Eight 7‐benzyl‐3‐tert‐butyl‐1‐phenylpyrazolo[3,4‐d]oxazines,encompassing structures containing no intermolecular hydrogen bonds,and hydrogen‐bonded structures in one,two or three dimensions

7‐Benzyl‐3‐tert‐butyl‐1‐phenyl‐6,7‐dihydro‐1H,4H‐pyrazolo[3,4‐d][1,3]oxazine, C₂₂H₂₅N₃O, (I), and 3‐tert‐butyl‐7‐(4‐methylbenzyl)‐1‐phenyl‐6,7‐dihydro‐1H,4H‐pyrazolo[3,4‐d][1,3]oxazine, C₂₃H₂₇N₃O, (II), are isomorphous in the space group P2₁, and molecules are linked into chains by C—H...O hydrogen bonds. In each of 3‐tert‐butyl‐7‐(4‐methoxybenzyl)‐1‐phenyl‐6,7‐dihydro‐1H,4H‐pyrazolo[3,4‐d][1,3]oxazine, C₂₃H₂₇N₃O₂, (III), which has cell dimensions rather similar to those of (I) and (II), also in P2₁, and 3‐tert‐butyl‐1‐phenyl‐7‐[4‐(trifluoromethyl)benzyl]‐6,7‐dihydro‐1H,4H‐pyrazolo[3,4‐d][1,3]oxazine, C₂₃H₂₄F₃N₃O, (IV), there are no direction‐specific interactions between the molecules. In 3‐tert‐butyl‐7‐(4‐nitrobenzyl)‐1‐phenyl‐6,7‐dihydro‐1H,4H‐pyrazolo[3,4‐d][1,3]oxazine, C₂₂H₂₄N₄O₃, (V), a combination of C—H...O and C—H...N hydrogen bonds links the molecules into complex sheets. There are no direction‐specific interactions between the molecules of 3‐tert‐butyl‐7‐(2,3‐dimethoxybenzyl)‐1‐phenyl‐6,7‐dihydro‐1H,4H‐pyrazolo[3,4‐d][1,3]oxazine, C₂₄H₂₉N₃O₃, (VI), but a three‐dimensional framework is formed in 3‐tert‐butyl‐7‐(3,4‐methylenedioxybenzyl)‐1‐phenyl‐6,7‐dihydro‐1H,4H‐pyrazolo[3,4‐d][1,3]oxazine, C₂₃H₂₅N₃O₃, (VII), by a combination of C—H...O, C—H...N and C—H...π(arene) hydrogen bonds, while a combination of C—H...O and C—H...π(arene) hydrogen bonds links the molecules of 3‐tert‐butyl‐1‐phenyl‐7‐(3,4,5‐trimethoxybenzyl)‐6,7‐dihydro‐1H,4H‐pyrazolo[3,4‐d][1,3]oxazine, C₂₅H₃₁N₃O₄, (VIII), into complex sheets. In each compound, the oxazine ring adopts a half‐chair conformation, while the orientations of the pendent phenyl and tert‐butyl substituents relative to the pyrazolo[3,4‐d]oxazine unit are all very similar.     

Different molecular conformations co‐exist in each of three 2‐aryl‐N‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)acetamides: hydrogen bonding in zero,one and two dimensions

4‐Antipyrine [4‐amino‐1,5‐dimethyl‐2‐phenyl‐1H‐pyrazol‐3(2H)‐one] and its derivatives exhibit a range of biological activities, including analgesic, antibacterial and anti‐inflammatory, and new examples are always of potential interest and value. 2‐(4‐Chlorophenyl)‐N‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)acetamide, C₁₉H₁₈ClN₃O₂, (I), crystallizes with Z′ = 2 in the space group P, whereas its positional isomer 2‐(2‐chlorophenyl)‐N‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)acetamide, (II), crystallizes with Z′ = 1 in the space group C2/c; the molecules of (II) are disordered over two sets of atomic sites having occupancies of 0.6020 (18) and 0.3980 (18). The two independent molecules of (I) adopt different molecular conformations, as do the two disorder components in (II), where the 2‐chlorophenyl substituents adopt different orientations. The molecules of (I) are linked by a combination of N—H…O and C—H…O hydrogen bonds to form centrosymmetric four‐molecule aggregates, while those of (II) are linked by the same types of hydrogen bonds forming sheets. The related compound N‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐yl)‐2‐(3‐methoxyphenyl)acetamide, C₂₀H₂₁N₃O₃, (III), is isomorphous with (I) but not strictly isostructural; again the two independent molecules adopt different molecular conformations, and the molecules are linked by N—H…O and C—H…O hydrogen bonds to form ribbons. Comparisons are made with some related structures, indicating that a hydrogen‐bonded R₂²(10) ring is the common structural motif.     

Hydrogen‐bonded assembly in six closely related pyrazolo[3,4‐b]pyridine derivatives; a simple chain,three types of chains of rings and a complex sheet structure

Six closely related pyrazolo[3,4‐b]pyridine derivatives, namely 6‐chloro‐3‐methyl‐1,4‐diphenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₄ClN₃O, (I), 6‐chloro‐3‐methyl‐4‐(4‐methylphenyl)‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₁H₁₆ClN₃O, (II), 6‐chloro‐4‐(4‐chlorophenyl)‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃Cl₂N₃O, (III), 4‐(4‐bromophenyl)‐6‐chloro‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃BrClN₃O, (IV), 6‐chloro‐4‐(4‐methoxyphenyl)‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₁H₁₆ClN₃O₂, (V), and 6‐chloro‐3‐methyl‐4‐(4‐nitrophenyl)‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃ClN₄O₃, (VI), which differ only in the identity of a single small substituent on one of the aryl rings, crystallize in four different space groups spanning three crystal systems. The molecules of (I) are linked into a chain of rings by a combination of C—H...N and C—H...π(arene) hydrogen bonds; those of (II), (IV) and (V), which all crystallize in the space group P, are each linked by two independent C—H...O hydrogen bonds to form chains of edge‐fused rings running in different directions through the three unit cells; the molecules of (III) are linked into complex sheets by a combination of two C—H...O hydrogen bonds and one C—H...π(arene) hydrogen bond; finally, the molecules of (VI) are linked by a single C—H...O hydrogen bond to form a simple chain.     

Synthesis and Structure of 3,4‐Dihydropyrido[2′,3′:3,4]pyrazolo[1,5‐a][1,3,5]triazin‐2‐amines

A new convenient synthon for heterocyclic chemistry, namely 1H‐pyrazolo[3,4‐b]pyridin‐3‐ylguanidine was successfully prepared by selective guanylation of 1H‐pyrazolo[3,4‐b]pyridin‐3‐amine. A series of 3,4‐dihydropyrido[2′,3′:3,4]pyrazolo[1,5‐a][1,3,5]triazin‐2‐amines was synthesized from 1H‐pyrazolo[3,4‐b]pyridin‐3‐ylguanidine using aldehydes or ketones as one‐carbon inserting reagents. The tautomeric preferences of the products were determined using spectroscopic (e.g., 2D NOESY NMR) and single crystal X‐ray diffraction data.