Alkylation of 1-Alkyl-3-methyl-1,4-dihydropyrazolo[4,3-<Emphasis Type="Italic">c</Emphasis>]pyrazoles with Halocarboxylic Acids Esters

A preparative method for the synthesis of 1-alkyl-3-methyl-1,4-dihydropyrazolo[4,3-c]pyrazoles was developed. The alkylation of the obtained compounds with halocarboxylic acid esters was also investigated. A principal possibility of creating libraries of compounds based on pyrazolo[4,3-c]pyrazole derivatives was shown.     

Synthesis of heterocyclic compounds from 4-formylpyrazoles

Formylation of pyrazole and 2,5-dimethylpyrazole gave a number of pyrazole-containing aldehydes, which can be used to obtain chromenes, tetrahydrochromenes, 1,4-dihydropyrano[2,3-c]pyrazoles, pyrano[3,2-c]chromenes, thiochromeno[4,3-b]pyrans, pyrano[3,2-c]-quinolines, and thiazolo[3,2-a]pyridines.     

Reactions with 5-aminopyrazoles. I. Synthesis of halogen-containing fused pyrazoles

5-Amino-3-phenylpyrazole (I) and 5-amino-4-bromo-3-phenylpyrazole (II) reacted with ethyl acetoacetate and acetylacetone to give various pyrazolo[1,5-a]pyrimidines IV-VI and with benzoins to give different fused pyrazoles, namely, imidazo[1,2-b]pyrazoles IX, pyrrolo[2,3-c]pyrazoles X and pyrazolo[4,3-b][1,4]oxazines XII. Diazotized II was coupled with active methylene-containing nitriles to afford pyrazolo[5,1-c]-as-triazines XIV.     

Oxidation and ring cleavage reactions of 3-benzhydrylchromones. Generation of triarylmethine cations from methylidenechroman-4-ones and benzopyrano[4,3-c]pyrazoles

The oxidation of 3-[bis-(diaryl)methyl]chromones 2 with p-chloranil affords novel acetals, 3-[bis-(diaryl)methylene]-2-methoxychroman-4-ones, 4 through interception of a pyrylium type intermediate. Oxidation of 3-(2-hydroxyphenyl)-4-[bis-(diaryl)methyl]pyrazoles 8, derived from 2 and hydrazines, gave 4,4-diarylbenzopyrano[4,3-c]pyrazoles 15. The electronic absorption spectra of 4 and 15 upon protonation are comparable with those of triarylmethine cationic dyes.     

A new strategy for the synthesis of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines and pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines

A series of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines were prepared via oxidative cyclization of aldehyde N-(1,3-diphenylpyrazolo[3,4-d]pyrimidin-4-yl)hydrazones. Dimroth rearrangement of such a series yielded pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines.     

Synthesis of 8,16-diarylacridino[4,3-<Emphasis Type="Italic">c</Emphasis>]acridine-1,9-dione derivatives

A number of new acridino[4,3-c]acridinedione derivatives have been synthesized for the first time by condensation of N¹,N⁵-bis(arylmethylidene)naphthalene-1,5-diamines with cyclic 1,3-diketones (cyclohexane-1,3-dione and dimedone). The product structure has been determined by two-dimensional NMR spectroscopy, and a probable reaction mechanism has been proposed.     

New polyazaheterocycles. 9-Methyl-di-s-triazolo[4,3-a:4,3-c]pyrimidine and 9-methyl-s-triazolo[4,3-c]tetrazolo[1,5-a]pyrimidine

9-Methyl-di-s-triazolo[4,3-a:4,3-c]pyrimidine and 9-methyl-s-triazolo[4,3-c]tetrazolo[1,5-a]pyrimidine have been synthetized from 4-hydrazino-7-methyl-s-triazolo[4,3-c]pyrimidine. Structural assignments based on nmr, ir and chemical manipulations are discussed.     

Synthesis and reactivity of 3-amino-1H-pyrazolo[4,3-c]pyridin-4(5H)-ones: development of a novel kinase-focussed library

3-Amino-1H-pyrazolo[4,3-c]pyridin-4(5H)-ones represent a potentially attractive heteroaromatic scaffold for drug-discovery chemistry. In particular, the arrangement of hydrogen bond donor and acceptor groups in the bicyclic core can fulfil the requirements for ATP competitive binding to kinase enzymes. Efficient and regioselective routes from simple starting materials to novel functionalised 3-amino-1H-pyrazolo[4,3-c]pyridin-4(5H)-ones and related 3-amino-2H-pyrazolo[4,3-c]pyridines were explored and adapted for parallel synthesis, resulting in a library of compounds suitable for screening against kinases and other cancer drug targets. Methods for substituent variation at five distinct positions around the bicyclic core were devised to generate sets of compounds containing two- or three-point diversity.     

Fused quinoline heterocycles X. First synthesis of new four heterocyclic ring systems 10-amino-6,9-disubstituted-[1,2,4]triazino[4′,3′:1,5]pyrazolo[4,3-c]quinoline derivatives

A novel, simple, and efficient synthetic methodology for the synthesis of hitherto unreported tetracyclic 10-amino-6,9-disubstituted-[1,2,4]triazino[4′,3′:1,5]pyrazolo[4,3-c]quinolines, in one step, has been developed by coupling of various active methylene compounds with diazotized heterocyclic amines. Reacting 2,4-dichloroquinoline-3-carbonitrile (1) with cyanoacetic acid hydrazide (2) in the presence of triethylamine in refluxing MeOH gave the unexpected 3-amino-4-chloro-1H-pyrazolo[4,3-c]quinoline (4), instead of the desired tetracyclic ring system 3 (Scheme 1). Refluxing 4 with excess of cyclic secondary amines 5a–c in boiling dimethylformamide yielded the corresponding 4-amino-pyrazolo[4,3-c]quinolines 6a–c. Diazotization of compounds 4 and 6a–c with sodium nitrite and concentrated HCl at ?5?°C gave the corresponding diazonium salts 17a–d, which were then subjected to couple with different active methylene nitriles, namely, 2-cyanothioacetamide (12), ethyl cyanoacetate (13), malononitrile (14), 2-cyanoacetamide (15), and 2-cyano-N-phenylacetamide (16), in aqueous ethanol containing sodium acetate as a buffer solution. The coupling reaction of diazonium salts 17 with 12, 13, and 14 leading to the novel perianellated tetracyclic ring system 10-amino-6,9-disubstituted-[1,2,4]triazino[4′,3′:1,5]pyrazolo[4,3-c]quinolines 19, 23, and 27, respectively, in one step, is described for the first time. On the other hand, coupling reaction of diazonium salt 17a with both 15 and 16 yielded the previously unknown tetracyclic 10-amino-6-chloro-[1,2,4]triazino[4′,3′:1,5]pyrazolo[4,3-c]quinoline-9-carboxamides 28a and 28b, respectively (Scheme 6). No chromatographic techniques have been used for the purification of the products. The structures of all the newly synthesized compounds were unambiguously confirmed by spectroscopic and analytical techniques.     

Some novel observations on the reaction of 2-hydrazino-3-methylquinoxaline with trifluoromethyl-β-diketones

The reaction of 2-hydrazino-3-methylquinoxaline 1 with trifluoromethyl-β-diketones 2 not only yields the expected 5-trifluoromethyl-5-hydroxy-Δ²-pyrazolines 3a-3f and/or 3-trifluoromethylpyrazoles 4c-4f but also the unexpected products 1,2,4-triazolo[4,3-a]quinoxalines 5a-5f and/or 3(5)-trifluoromethyl-1H-pyrazoles 6c-6f. Furthermore, the acid-catalyzed dehydration of 5-hydroxypyrazolines 3a-3b resulted in the formation of unexpected 5a-5b along with the expected corresponding pyrazoles 7a-7b. These unprecedented observations provide evidence for the existence of equilibrium between the hydroxypyrazoline 3 and its open chain tautomer, ketoimine 9 in the mechanistic path leading to the formation of pyrazoles 7 and triazoles 5.     

Condensed Pyridopyrimidines. 7. Synthesis of Condensed Triazolo[4,3-c]- and Tetrazolo[1,5-c]pyrimidines

Novel dihydro-5H-pyrano[3',4':5',6']pyrido[2,3-d]-1,2,4-triazolo[4,3-c]pyrimidines and 1,2,3,4-tetrazolo[1,5-c]pyrimidines have been synthesized from 2-amino-3-cyano-7,7-dimethyl-7,8-dihydro-5H-pyrano[4,3-b]pyridine.     

Preparation of novel pyridine-fused tris-heterocycles; pyrido[4,3-e]pyrrolo-/pyrido[4,3-e]furano[2,3-c]pyridazines and pyrido[3,4-b]pyrrolo[3,2-d]pyrrole

Three novel pyrido-fused tris-heterocycles have been prepared based on a Suzuki coupling and subsequent cyclisation approach. Pyrido[4,3-e]pyrrolo[2,3-c]pyridazine (3b, 77%) and pyrido[4,3-e]furano[2,3-c]pyridazine (5b, 76%) were obtained by intramolecular diazocoupling. Successful diazocoupling of furan (5b) is thus reported for the first time by NOBF₄ generation of the diazonium intermediate. N-TIPS-pyrido[3,4-b]pyrrolo[3,2-d]pyrrole (TIPS-4b) was synthesised by thermal cyclisation of pyridyl nitrene in considerably higher yield (71%) than previously experienced from similar cyclisations, due to TIPS-activation.     

Regioselective synthesis of 2,5-dihydro-4H-pyrazolo[4,3-c]quinolin-4-ones by the cyclization of 3-acyl-4-methoxy-1-methylquinolinones with hydrazines

Reaction of 3-acyl-4-methoxy-1-methylquinolinones 2 and 5 with hydrazines has been investigated under different experimental conditions. Compound 2 always gave rise selectively and exclusively to the regioisomeric 1,3-disubstituted- or 2,3-disubstituted-pyrazolo[4,3-c]quinolin-4(5H)one (compounds 3a,b or 4a,b, respectively), while reaction of 5 with N-methylhydrazine led to a mixture of pyrazoles 7a and 8a. With N-phenylhydrazine, compounds 7b or 8b were regioselectively obtained. Compound 8a could be selectively synthesized working in solventless conditions. Structural elucidation of all products was independently achieved by NMR spectroscopy.     

Angular Regioselectivity in the Reactions of 2-Thioxopyrimidin-4-ones and Hydrazonoyl Chlorides: Synthesis of Novel Stereoisomeric Octahydro[1,2,4]triazolo[4,3-a]quinazolin-5-ones

The regioselective synthesis of cis and trans stereoisomers of variously functionalized octahydro[1,2,4]triazolo[4,3-a]quinazolin-5-ones was performed. The 2-thioxopyrimidin-4-ones used in the synthesis reacted with hydrazonoyl chlorides in a regioselective manner to produce the angular regioisomers [1,2,4]triazolo[4,3-a]quinazolin-5-ones rather than the linear isomers [1,2,4]triazolo[4,3-a]quinazolin-5-ones. The synthesis process took place with electronic control. The angular regiochemistry of the products was confirmed by X-ray experiments and two-dimensional NMR studies.     

Microwave-assisted organocatalytic multicomponent Knoevenagel/hetero Diels-Alder reaction for the synthesis of 2,3-dihydropyran[2,3-c]pyrazoles

A rapid protocol for the multicomponent microwave-assisted organocatalytic domino Knoevenagel/hetero Diels-Alder reaction (DKHDA) has been developed for the synthesis of 2,3-dihydropyran[2,3-c]pyrazoles. The reported procedure could be used for the fast generation of novel substituted 2,3-dihydropyran[2,3-c]pyrazoles with potential anti-tuberculosis activity.     

Synthesis of derivatives of pyrazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidines and imidazo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidines proceeding from alkyl 2-benzylidene-3-oxo-3-fluoroalkylpropionates

Methods were developed of the synthesis of alkyl 2-hydroxy-2-fluoroalkyl-4-phenyl-1,2,3,4—tetrahydroimidazo-[1,5-a]pyrimidine-3-carboxylates and alkyl-5-hydroxy-2,7-diphenyl-5-fluoroalkyl-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidine-6-carboxylates by regioselective [3+3]-cycloaddition of 5-aminoimidazole or 5-aminopyrazole to alkyl 2-benzylidene-3-oxo-3-fluoroalkylpropionates at the fluoroacylvinyl fragment.     

Fluorine-containing heterocycles: XVI. Reactions of tetrafluorobenzoyl isothiocyanate with hydrazines and their derivatives

Fluorinated derivatives of 4H-1,3-benzothiazin-4-one, [1,2,4]triazolo[4,3-a]pyrimidine, [1,2,4]triazolo[3,4-b][1,3]benzazoles, and 1,5-dihydro-1,2,4-triazole-5-thione were synthesized by addition of hydrazines and their derivatives to tetrafluorobenzoyl isothiocyanate, followed by cyclization of intermediate thiosemicarbazides.     

Synthesis and reactivity of 1,2,4-triazolo[1,5-c]quinazolines

The preparation of 1,2,4-triazolo[1,5-c]quinazolines 4a-d , 5 , 8a-d by cyclocondensation of 1a-c with carboxylic acids and carboxylic anhydrides, respectively, is described. By different pathways, the 5-thioxo-5,6-dihydro-1,2,4-triazolo[1,5-c]quinazolines 4a-d react with hydrazine hydrate or amines with the formation of 5-substituted 1,2,4-triazolo[1,5-c]quinazolines 9 and 10a-d . Cyclocondensation of 9 with carboxylic acids, carboxylic anhydrides, and nitrous acid, respectively, leads to the new anellated heterocycles bis-1,2,4-triazolo[4,3-a:1,5-c]quinazoline 13 and tetrazolo [1,5-a]-1,2,4-triazolo[1,5-c]quinazoline ( 14 ).     

Synthesis of New Heterocyclic Systems on the Basis of 7-Benzyl-3-chloro-1-(morpholin-4-yl)-5,6,7,8-tetrahydro-2,7-naphthiridine-4-carbonitrile

Methods have been developed for the synthesis of new 8-amino-3-benzyl-5-(morpholin-4-yl)-1,2,3,4-tetrahydropyrimido[4′,5′: 4,5]thieno[2,3-c][2,7]naphthyridine starting from 7-benzyl-3-chloro-1-(morpholin-4-yl)-5,6,7,8-tetrahydro-2,7-naphthyridine-4-carbonitrile. 8-Hydrazinyl-3-benzyl-5-(morpholin-4-yl)-1,2,3,4-tetrahydropyrimido[4′,5′: 4,5]thieno[2,3-c][2,7]naphthyridine has been converted to isomeric pentacyclic structures with a triazole ring fused through the [c] side of the pyrimidine ring, and their Dimroth rearrangement has been accomplished in both acidic and basic media. New heterocyclic systems containing pyrrolo[1,2-a]pyrimidinone and pyrimido[1,2-a]azepinone fragments were obtained on the basis of the thieno-[2,3-c][2,7]naphthyridine derivative.     

Methyl (5-oxopyrazol-3-yl)acetate <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">S</Emphasis>-ketene acetal as a new building block for the construction of pyrazolo[4,3-<Emphasis Type="Italic">c</Emphasis>]pyridines

Methyl (5-oxopyrazol-3-yl)acetate is added to methylthiocyanate C≡N bond in the presence of Ni(OAc)₂ giving a corresponding heterocyclic N,S-ketene acetal. The latter compound was used as a convenient synthon in the synthesis of new pyrazolo[4,3-c]pyridin-3-ones and pyrazolo[4,3-c]pyridine-3,6-diones.