Heterocyclic synthesis via enaminones: Regioselective synthesis of some novel pyrazole,isoxazole, pyrimidine,pyrido[1,2‐a]benzimidazole and pyrazolo[1,5‐a]‐pyrimidine derivatives

2‐Acetylbenzothiazole ( 1 ) reacts with dimethylformamide dimethylacetal (DMF‐DMA) to afford the enaminone 2. Compound 2 reacts regioselectively with some nitrilimines 5a–d and nitrile oxides 6b–d to afford the novel pyrazole and isoxazole derivatives 11a–d and 12b–d, respectively, which react with hydrazine hydrate to give the new pyrazolo[3,4‐d]pyridazine and isoxazolo[3,4‐d]pyridazine derivatives 13a–d and 14b–d, respectively. The enaminone 2 reacts with 1H‐benzimidazole‐2‐acetonitrile ( 17 ) to afford the pyrido[1,2‐a]benzimidazole derivatives 19. Compound 2 reacts also with 5‐amino‐3‐phenylpyrazole ( 20 ) and with guanidine to afford the new pyrazolo[1,5‐a]pyrimidine and the 2‐aminopyrimidine derivatives 22 and 24, respectively. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 417–422, 1999     

Synthesis and biological activities of some new thiazolidine derivatives containing pyrazole ring system

As a part of systematic investigation of synthesis and biologically active compounds of thiazolidine (TZD) derivatives containing pyrazole ring system, several new pyrazole–TZD derivatives 8a , 8b , 8c , 8d and 9a , 9b , 9c , 9d have been synthesized. Compounds 8a , 8b , 8c , 8d were prepared from N‐substituted TZDs 6a , 6b , 6c , 6d and 1H‐pyrazole‐4‐carboxaldehyde 7 by Knoevenagel‐type reaction. Treatment of 8a , 8b , 8c , 8d with sodium hydride at room temperature caused dimerization reaction to afford the corresponding spirocompounds 9a , 9b , 9c , 9d . All the synthesized compounds were characterized by spectroscopic analysis. In vitro, the synthesized compounds 8a , 8b , 8c , 8d and 9a , 9b , 9c , 9d were tested for their growth inhibitory activity in A549 lung cancer, B16F10 murine melanoma, and HeLa human uterine carcinoma cells and for their differentiation of 3T3‐L1 preadipocytes to adipocytes. The results showed that compound 8c possessed growth inhibitory effect of B16F10 cells (IC₅₀ = 27 μM) and compounds 9c , 9d had induction effect on the differentiation of 3T3‐L1 preadipocytes. J. Heterocyclic Chem., (2011).     

Synthesis with nitriles: synthesis of some new mercaptopyridazine, mercaptopyridazino[1,6-a]quinazoline and thiophene derivatives

2-(1-(4-Bromophenyl)-2-thiocyanatoethylidene)malononitrile (3) undergoes azo coupling with diazotized aromatic amines to afford arylhydrazone derivatives, which are readily cyclized to afford the corresponding 3(2H)-pyridazinimine derivatives upon reflux in aqueous NaOH. Under similar condition an o-cyanoarylhydrazone derivative was cyclized into 6H-pyridazino[1,6-a]quinazolin-6-imine, which in turn was easily transformed into 6H-pyridazino[1,6-a]quinazolin-6-one on reflux in ethanolic/HCl. Compound 3 afforded substituted 5-acetylthiophene derivatives upon reflux in AcOH/HCl mixtures.     

Synthesis,characterization, and biological activity of some aza‐uracil derivatives

Thiation of 1 by LR gave the corresponding 3,5‐dithioxo derivative 2 and the trimer 3 . Methylation of 1 afforded the S‐methyl derivative 4 . Compound 1 was fused with 6‐bromo‐2‐phenyl‐benzo[1,3‐d]oxazin‐4‐one ( 5 ) and gave 6 . Condensation of 1 with some acid derivatives 7a , 7b , 7c , 7d and/or 8a , 8b , 8c yielded thiadiazolo‐triazine derivatives 9a , 9b , 9c , 9d and 10a , 10b , 10c . Compounds 9a , 9c and 10c were hydrolyzed to furnish 11a , 11b , 11c Acetylation of 14 afforded mono‐ and diacetyl‐derivatives 15 and 16 . Benzoylation of 14 afforded mono‐ and dibezoyl‐derivatives 17 and 18 . 14 with some aromatic aldehydes yielded 9a , 9b , 9c . Reacting 14 with phenyl (iso‐ and/or isothio‐) cyanate gave the urea derivatives 20a , 20b . Thiation of 14 with P₄S₁₀ furnished 21 . The newly synthesized compounds were tested as antimicrobial agents. J. Heterocyclic Chem., (2011)     

Studies with enaminones: The reaction of enaminones with aminoheterocycles. A route to azolopyrimidines,azolopyridines and quinolines

The enaminones 1b,d,f react with 4‐phenyl‐3‐methyl‐5‐pyrazoleamine 3a to yield the pyrazole derivatives 4a‐c that cyclised readily on reflux in pyridine solution in presence of hydrochloric acid to yield the pyrazolo[1,5‐a]pyrimidines 5a‐c. Similarly 3(5)‐amino‐1H‐triazole (3b) reacted with 1b,d,f to yield the triazolo[1,5‐a]pyrimidines 5d‐f. In contrast attempted condensation of the 5‐tetrazoloamine (3c) with 1a,d,e resulted in its trimerisation and only triaroylbenzene 8a,d,e was isolated. The reaction of 1a,b,d with anthranilonitrile 9a and the reaction of 1a‐c with the 2‐aminocyclohexene thiophene‐3‐nitrile 10a afforded the cis enaminones 11a‐c and 12a‐c. Similarly, reaction of 1a‐c with the methylanthranilate 9b and reaction of 1b,e with ethyl 2‐aminocyclohexene thiophene‐3‐carboxylate 10b afforded the cis enaminones 11d‐f and 12d,e respectively. Attempted cyclization of 11a‐c into quinoline failed. Successful cyclization of 11d into the quinolinone 13 could be affected, on heating for five minutes in a domestic microwave oven at full power. The reaction of 1a‐c,f with piperidine afforded the trans enaminones 14a‐d. Similarly, trans 14e was formed from the reaction of 1b with morpholine. The coupling reaction of 1b with excess of benzene diazonium chloride afforded the formazane 16. The enaminone 2 reacted with heterocyclic amines to yield the pyridones 17,18.     

Regioselective synthesis of some novel pyrazoles,isoxazoles, pyrazolo[3,4‐d]pyridazines and isoxazolo[3,4‐d]pyridazines pendant to benzimidazole

2‐Acetyl‐1‐methyl‐1H‐benzimidazole reacts with dimethylformamide‐dimethyl‐acetal (DMF‐DMA) to afford the corresponding E‐1‐(1‐methyl‐1H‐benzimidazol‐2‐yl)‐3‐N,N‐dimethylaminoprop‐2‐enone. The latter compound reacts regioselectively with some nitrilimines and nitrile oxides to afford the corresponding pyrazole and isoxazole derivatives, respectively. These reaction products react with hydrazine hydrate to give the novel pyrazolo[3,4‐d]pyridazine and isoxazolo[3,4‐d]pyridazine derivatives, respectively.     

Indolizines,triazolo[4,3‐a]pyridines,benzimidazo[1,2‐d]oxadiazoles,and pyrazolo[1,5‐c]triazoles via nitrogen and sulfur ylides

The pyridinium salts 2a,b reacted with dimethyl acetylenedicarboxylate (DMAD) to give the indolizine derivatives 6a,b . Pyridinium salts 2a,b also reacted with pyrazole‐5‐diazonium salt to afford the hydrazonoyl bromides 8a,b , which on treatment with aqueous ethanolic sodium carbonate furnished the 8aH‐1,2,4‐triazolo[4,3‐a]pyridine 10 . When sulfonium bromide 11 was treated with nitrous acid and with pyrazole‐5‐diazonium salt, it afforded the new hydroximoyl and hydrazonoyl halides 12 and 17 , respectively. Compound 12 reacted with 2‐methylthiobenzimidazole to furnish benzimidazo[1,2‐d]‐1,2,4‐oxadiazole derivative 14 . Treatment of either 12 with 3‐phenyl‐5‐aminopyrazole or 17 with triethylamine resulted in the formation of the same product: pyrazolo[1,5‐c]‐1,2,4‐triazole derivative 16 . © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:432–436, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20037     

Synthesis and Reactions of Some Heterocyclic Candidates Based on 2‐Amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene Moiety as Anti‐Arrhythmic Agents

In continuation of our previous work, a series of novel thiophene derivatives 4 , 5 , 6 , 8 , 9 , 9a , 9b , 9c , 9d , 9e , 10 , 10a , 10b , 10c , 10d , 10e , 11 , 12 , 13 , 14 , 15 , 16 were synthesized by the reaction of ethyl 2‐amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐3‐carboxylate ( 1 ) or 2‐amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐3‐carbonitrile ( 2 ) with different organic reagents. Fusion of 1 with ethylcyanoacetate or maleic anhydride afforded the corresponding thienooxazinone derivative 4 and N‐thienylmalimide derivative 5 , respectively. Acylation of 1 with chloroacetylchloride afforded the amide 6 , which was cyclized with ammonium thiocyanate to give the corresponding N‐theinylthiazole derivative 8 . On the other hand, reaction of 1 with substituted aroylisothiocyanate derivatives gave the corresponding thiourea derivatives 9a , 9b , 9c , 9d , 9e , which were cyclized by the action of sodium ethoxide to afford the corresponding N‐substituted thiopyrimidine derivatives 10a , 10b , 10c , 10d , 10e . Condensation of 2 with acid anhydrides in refluxing acetic acid afforded the corresponding imide carbonitrile derivatives 11 , 12 , 13 . Similarly, condensation of 1 with the previous acid anhydride yielded the corresponding imide ethyl ester derivatives 14 , 15 , 16 , respectively. The structures of newly synthesized compounds were confirmed by IR, ¹H NMR, ¹³C NMR, MS spectral data, and elemental analysis. The detailed synthesis, spectroscopic data, LD₅₀, and pharmacological activities of the synthesized compounds are reported.     

Synthesis and Antimicrobial Activity of Some Novel Substituted Bis‐Pyridone,Pyrazole, and Thiazole Derivatives

A variety of novel bis‐heterocyclic derivatives were synthesized via the reaction of bis‐cyanoacetanilide derivative 3 with various aromatic aldehydes (1:2 molar ratio), to give the corresponding bis‐arylidene derivatives 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 5k , 5l , 5m . On the other hand, reacting compound 3 with substituted 2‐hydroxybenzaldehydes 6a , 6b , 6c afforded 2‐iminochromene‐3‐carboxamides 7a , 7b , 7c . The reaction of compound 5 with malononitrile afforded the novel bis‐pyridones 9a , 9b , 9c , 9f , 9g , 9h . The reaction of 5 with hydrazine derivatives afforded pyrazoles 11a , 11b , 11c , 11d , 11e , 11f , respectively. Compound 3 reacts with phenyl isothiocyanate in the presence of potassium hydroxide at room temperature followed by addition of some different halo‐carbonyl compounds to afford bis‐poly‐functionalized thiazole derivatives 13a , 13b , 13c . The bis‐enamine derivative 15 reacts also with hydrazine hydrate, guanidine, and hydroxylamine to give bis‐pyrazole 17 , pyrimidine 19 , and isoxazole 21 derivatives, respectively. Some of the newly synthesized compounds show moderate to high antimicrobial activity.     

Synthesis of Some Novel Heterocyclic Xylidinyl Amines and Carboxamides

The xylidines 1a , 1b undergo condensation with ethyl cyanoacetate 2 and ethyl benzoyl acetate 15 to afford the cyano acetanilides 3a , 3b and the β‐diketones 16a , 16b , respectively. Compounds 3a , 3b react with hydrazine and phenyl hydrazine to afford the azine‐bis derivatives 5a , 5b and 7a , 7b , whereas 16a , 16b react with the same reagents to afford the pyrazolyl amine derivatives 17a , 17b and 18a , 18b , respectively. Compounds 3a , 3b react also with dimethylformamide dimethylacetal to afford the enaminonitriles 8a , 8b , whereas 16a , 16b react with the same reagent to afford only the enaminone 19b . The enaminonitriles 8a , 8b react with hydrazine and phenyl hydrazine to afford also the azine‐bis derivatives 11a , 11b and 14a , 14b , respectively.     

A Novel Synthesis of Some 1,4‐Phenylene‐bis‐heterocyclic Derivatives and of Some Pyran,Pyrano[2,3‐c]pyrazole,and Pyrano[2,3‐d]pyrimidine Derivatives [1]

p‐Diacetyl benzene 1 undergoes bromination to afford p‐bromoacetyl phenacyl bromide 2 . Compound 2 reacts with twofold excess of malononitrile to afford 2‐{2‐[4‐(3,3‐Dicyanopropionyl)‐phenyl]‐2‐oxo‐ethyl}‐malononitrile 3 . Compound 3 could be cyclized to afford the 1,4‐phenylene‐bis‐furan derivative 4 . Compound 3 reacts also with a twofold excess of hydrazine hydrate and phenyl hydrazine under dry conditions at RT to afford the bis‐pyrazole derivatives 5a , 5b , respectively. The reaction of 5a , 5b with the same reagents in refluxing dioxane afforded the bis‐pyrazolopyridazine derivatives 7a , 7b , respectively. The azo coupling of compound 3 with arene diazonium salts afforded the bis‐pyrazole derivatives 9a , 9b , 9c . The β‐keto esters 10a , 10b react with benzaldehyde and malononitrile in a one pot synthesis to afford the pyran derivatives 11a , 11b . These latter compounds react with hydrazine hydrate and urea derivatives to afford the pyrano[2,3‐c]pyrazoles 15a , 15b and the pyrano[2,3‐d]pyrimidine derivatives 17a , 17b , respectively.     

Synthesis,Reactions, and Pharmacological Evaluations of Some Novel Pyridazolopyridiazine Candidates

Herein, we report the synthesis, characterization, and preliminary pharmacological activity of a new series of substituted pyrazolopyridazine derivatives. Compound 1 was reacted with ethoxymethylene malononitrile 2 in refluxing ethanol to give the corresponding compound 3 , which was treated with hydrazine hydrate or formamide to give pyrazolo[3,4‐c]pyrazole 4 and pyrazolo pyrimidine 5 derivatives, respectively. Also, compound 3 was reacted with NH₄SCN or carbon disulphide or ethyl acetoacetate to yield the corresponding pyrazolo derivatives 6 , 7 , 8 , respectively. Additionally, compound 3 was reacted with triethyl orthoformat in acetic anhydride to give 9 , which was treated with hydrazine hydrate to give hydrazino derivative 10 . The latter compound transformed into the pyrazolo[4,3‐e][1,2,4]triazolo[1,5‐c]‐pyrimidine 11 via refluxing with acetic anhydride. Finally, compound 9 was reacted with benzoic acid hydrazide or mercapto acetic acid to give compounds 12 and 13 , respectively. The latter compound was treated with refluxing ethanolic sodium ethoxide solution to afford the pyrazolothiazolopyrimidine 14 . Some of the compounds exhibited better activities as anti‐inflammatory and antimicrobial agents than the reference controls. The detailed synthesis, spectroscopic data, anti‐inflammatory, and antimicrobial activities of the synthesized compounds was reported.     

2‐Pyrazolin‐5‐One‐Based Heterocycles: Synthesis and Characterization

A novel series of pyrazoline and thiazole derivatives incorporating 2‐pyrazolin‐5‐one moiety were synthesized starting from α,β‐unsaturated ketones under the effect of hydrazine derivatives and thiosemicarbazide. The obtained pyrazolines 4a , 4b were treated with different reagents to afford N‐substituted pyrazolines 5a , 5b , 6a , 6b , 7a , 7b , 8a , 8b . N‐Thiocarbamoyl pyrazolines 12a , 12b were cyclized using phenacyl bromide, 2,3‐dichloroquinoxaline, and monochloroacetic acid afforded the novel pyrazolinyl thiazoles 13a , 13b , 14a , 14b , 15a , 15b , 16a , 16b , 16c , 16d , 16e , 16f . The newly synthesized compounds were characterized by analytical and spectral data.     

Antimicrobial Activity of Some Novel Thiourea,Hydrazine, Fused Pyrimidine and 2‐(4‐Substituted)anilinobenzoazole Derivatives Containing Sulfonamido Moieties

Thiophosgenation of sulfonamides 1a‐c in the presence of dilute HCl at room temperature furnished the isothiocyanatosulfonamides 2a‐c and treatment with aromatic amines gave 1,3‐disubstituted thioureas 3a,b . Also, interaction of two molecules of 2c with 1,4‐phenylenediamine yielded the novel bisthiourea 4 . Cyclocondensation of 2 with ortho amino carboxylic acid compounds such as anthranilic acids 8 , 5‐amino‐1‐phenyl‐pyrazol‐4‐carboxylic acid 9 and 4,5,6,7‐tetrahydro‐2‐amino‐benzo[b]thiophene‐3‐carboxylic acid 10 furnished the fused thiopyrimidines 11a‐d, 12 and 13 , respectively. 2‐Anilinobenzoazole derivatives 15a‐c, 16a, b and 17a,b were obtained through cyclocondensation of 2 with 1,2‐dinucleophiles.     

Synthesis and reactivity of cyanomethyl 2‐amino‐4‐methylthiazolyl ketone. A facile synthesis of novel pyrazolo[5,1‐c]1,2,4‐triazine, 1,2,4‐triazolo[5,1‐c]1,2,4‐triazine, 1,2,4‐triazino[4,3‐a]benzimidazole,pyridazine‐6‐imine and 6‐oxopyridazinone derivatives

The novel and versatile cyanomethyl 2‐amino‐4‐methylthiazolyl ketone (5) was prepared by treatment of bromomethyl 2‐amino‐4‐methyl thiazolyl ketone (4) with potassium cyanide. Reaction of 5 with heterocyclic diazonium salts 6a,b and 10 afforded the corresponding hydrazones 7a,b and 11, respectively. Refluxing of the hydrazones in pyridine afforded the corresponding pyrazolo[5,1‐c]‐1,2,4‐triazine, 1,2,4‐triazolo[5,1‐c]‐1,2,4‐triazine, and 1,2,4‐triazolo[4,3‐a]benzimidazole derivatives 8a,b and 12, respectively, via intramolecular cyclization. Compound 5 coupled also with benzenediazonium chloride to afford the corresponding hydrazone 14, which is an excellent precursor for the synthesis of pyridazine‐6‐imine 17a and pyridazinone 17b. The pyridazine derivatives 17a,b were also prepared by an independent route, that is, the condensation with malononitriles and coupling with benzenediazonium chloride, followed by intramolecular cyclization. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 385–390, 1999     

One‐pot Synthesis of 1,2,3,4‐Tetrahydropyrimidin‐2(1H)‐thione Derivatives and their Biological Activity

2‐Thioxo/oxo‐1,2,3,4‐tetrahydropyrimidine‐5‐carboxylate derivatives 2a , 2b , 2c , 2d were prepared by the reaction of ethyl acetoacetate and thiourea or urea with aldehydes using NH₄Cl as a catalyst. Compounds 2a and 2c reacted with mono and bihalogenated compounds such as ethyl iodide, chloroacetonitrile, epichlorohydrin, acetyl chloride, ethyl bromoacetate, chloroacetic acid, chloroacetylchloride, and/or oxalyl chloride to afford compounds 3 , 4a , 4b , 5 , 6a , 6b , 7 , 8 , 9 and 10 , respectively. Compounds 2a , 2c , and 7 were allowed to react with p‐fluorobenzaldehyde to yield the corresponding products 11a , 11b , and 12 , respectively. Oxidation of 2a and 2c gave 2b , 13a , 13b , 14 , 15 , 16 dependent on the oxidizing agent used. Vilsmeiere‐Haack formylation of 2a and 2b with POCl₃/DMF afforded 17a and 17b . Chlorination of 2b and 2d gave the chlorinated derivative 18a and 18b , which reacted with thiourea to give thioureidopyrimidine 19a and 19b . Reactions of 2a with hydrazine monohydrate, semicarbazide hydrochloride, and sodium hydroxide gave compounds 20 , 21 , 22 , respectively. The cytotoxicity and in vitro anticancer evaluation of some prepared compounds have been assessed against two different human tumor cell lines including breast adenocarcinoma MCF‐7 and human hepatocellular carcinoma HepG2. Antimicrobial and antioxidant activities of some compounds were investigated. The newly synthesized compounds were characterized by IR, ¹H‐NMR, ¹³C‐NMR, and mass spectral data.     

A New and Facile Synthesis of Novel Pyrazolothienopyrimidines and Imidazopyrazolothienopyrimidines

4‐Amino‐3‐methyl‐1‐phenyl‐1H‐thieno[2,3‐c]pyrazole‐5‐carboxamide ( 5 ), which was synthesized by an innovative method, was used as a versatile precursor for synthesizing pyrazolothienopyrimidines and imidazopyrazolothienopyrimidines compounds. Reaction of amino thienopyrazole carboxamide 5 with triethyl orthoformate afforded thienopyrazolopyrimidine 6 . Chlorination of the latter compound, using phosphorus oxychloride afforded the chloro pyrazolothienopyrimidine 7 , which underwent nucleophilic substitution reactions with various primary and secondary amines to give the alkyl (aryl) amino pyrimidine compounds 8a–d . On the other hand, the reaction of chloropyrimidine 7 with thiourea afforded the pyrimidine thione compound 9 , which was alkylated with α‐halogentaed compounds to afford the S‐alkylated derivatives 10a–c . Also, chloroacetylation of the amino carboxamide 5 using chloroacetyl chloride yielded the chloromethyl pyrazolothienopyrimidine 12 , which underwent nucleophilic substitu‐ tion reactions with various primary and secondary amines to afford the alkyl (aryl) aminomethyl compounds 13a–f . The latter Compounds underwent Mannich reaction to give imidazopyrimidothieno‐ pyrazoles 14a–c . The newly synthesized compounds and their derivatives were fully characterized by elemental and spectral analysis.     

Synthesis of Some New Pyrazole,Pyrimidine, Pyridazine,and Their Fused Derivatives from 3‐Oxo‐3,N‐diphenylpropionamide

The title compounds were obtained from the reactions of 3‐oxo‐3,N‐diphenylpropionamide 3 with dimethylformamide dimethylacetal followed by hydrazine to afford the pyrazole 7 , condensation with benzaldehyde followed by cyclocondensation with guanidine to afford the pyrimidine derivative 13 , condensation with active methylenes followed by azo coupling of the products followed by cyclization to afford the pyridazines 17a , 17b . The pyridazinone 17b was explored for the synthesis of some novel pyridazine‐fused heterocyclic compounds 19 , 21 , 24a , 24b , 24c , and 26 . All structures were proved via their elemental analyses and spectral data.     

Synthesis of Some New Benzimidazole–Thiazole Derivatives as Anticancer Agents

4‐(1H‐benzo[d]imidazol‐2‐yl)thiazol‐2‐amine and its 1‐methyl derivative ( 1 ) were reacted with different reagents such as acid anhydrides, malononitrile, chloroacetyl chloride, and aromatic aldehydes to produce the corresponding benzimidazole products 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , respectively. Also, 2‐chloro‐N‐(4‐(1‐methyl‐1H‐benzo[d]imidazol‐2‐yl)thiazol‐2‐yl) acetamide ( 6 ) was reacted with diaminoethane, ortho‐substituted aniline, thioglycolic acid, thiosemicarbazide derivatives, secondary amines, and potassium isothiocyanate to afford the corresponding derivatives 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , respectively. The cytotoxic activity of some newly synthesized derivatives was studied against two different cell lines HepG2 and PC12. Compounds 9 and 15b showed promising anticancer activity against both types of the tested cancerous cell lines.     

Facile synthesis of some novel pyrrole and pyridazinoquinazolone derivatives

3-Dicyanomethylene-3-phenylpropionitrile coupled with diazotized aromatic amines (Ar-NH₂) to afford hydrazono derivatives. The latter (Ar = C₆H₅, 4-CH₃C₆H₄, 4-CH₃OC₆H₄, and 4-ClC₆H₄) were readily cyclized upon reflux in aqueous NaOH to 3(2H) pyridazinimine derivatives, which were readily transformed into their corresponding pyridazinone derivatives on reflux in ethanolic HCl. The pyridazinimines undergo reductive cleavage and recyclization via loss of ammonia to afford the corresponding N-aryl pyrroles on reflux in glacial acetic acid with Zn dust. The pyridazinone derivatives, however, undergo the same reaction but with loss of the aromatic amine moiety to afford only one pyrrolone derivative. The hydrazono derivative (Ar = 2-NCC₆H₄) was cyclized into pyridazino[3,2-b]quinazolin-6-imine, which is easily converted into pyridazino[3,2-b]quinazolin-6-one on reflux in ethanolic HCl. The latter compound is also obtained from the hydrazo derivatives (Ar = 2-HOOCC₆H₄ and 2-MeOOCC₆H₄) by reflux in aqueous NaOH.