Synthesis and Reactions of 3‐Methylthiazolo[3,2‐a]Benzimidazole‐2‐Carboxylic Acid Hydrazide: Synthesis of Some New Pyrazole, 1,3‐Thiazoline, 1,2,4‐Triazole and 1,2,4‐Triazolo[3,4‐b]‐1,3,4‐Thiadiazine Derivatives Pendant to Thiazolo[3,2‐a]Benzimidazole Moiety

The reaction of 3‐methylthiazolo[3,2‐a]benzimidazole‐2‐carboxylic acid ethyl ester (1) with hydrazine hydrate gives the hydrazide 2 which reacts with CS₂/KOH to afford the potassium salt 3. Treatment of 3 with l‐aryl‐2‐bromoethanones 4a,b afforded the 1,3‐thiazoline derivatives 6a,b, respectively, while the reaction of 3 with hydrazine hydrate afforded 1,2,4‐triazole‐3‐thione derivative 9. The reaction of 9 with l‐aryl‐2‐bromoethanones 4a,b and with hydrazonyl chlorides 11a,b gave the 1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazine derivatives 10a,b and 12a,b, respectively. Treatment of hydrazide 2 with phenyl isothiocyanate in refluxing benzene gave the thiosemicarbazide derivative 16. The latter reaction gave 1,3,4‐oxadiazole derivative 17 when benzene was replaced by DMF. Cyclization of the thiosemicarbazide derivative 16 with NaOH resulted in the formation of the 1,2,4‐triazole‐3‐thione derivative 18.     

Synthesis of Newly Substituted Pyrazoles and Substituted Pyrazolo[3,4‐b]Pyridines Based on 5‐Amino‐3‐Methyl‐1‐Phenylpyrazole

The reaction of the aminopyrazole 1 with benzenesulfonyl chloride, arenediazonium salt, chloroacetyl chloride, ethoxy methyleneamlononitrile and with ethyl 2‐cyano‐3‐ethoxyacrylate gave the substituted 3‐methyl‐1‐phenylpyrazole 2–5a,b . Compound 5b was cyclized to 6 and to 7 by treating it with AlCl₃ and with POCl₃, respectively. Compound 6 converted to 7 by boiling it in POCl₃/PCl₅. Compound 10b was produced through reaction of 9 with acetophenone. Reaction of 1 with benzylidinemalononitrile afforded 11 . New methods for preparation of 15 and 16 are described. The reaction of 8 with malononitrile, thiosemicarbazide, phenyl hydrazine and acetophenone afforded compounds 18–21 . The reaction of 21 with malononitrile gave 22 . Compounds 23–26 were produced upon reaction of 10a with malononitrile, phenyl hydrazine, thiosemicarbazide, semicarbazide and with benzaldehyde, respectively.     

One‐Pot Green Synthesis of Thiazolo[3,2‐a]pyridine Derivatives via Tandem Cyclization in Aqueous Media

Facile, three‐component domino reactions of readily available thioglycolic acid/ethyl thioglycolate, aromatic aldehydes, and malononitrile/ethyl cyanoacetate in aqueous potassium carbonate at room temperature afforded thiazolo[3,2‐a]pyridine derivatives chemoselectively in good to excellent yield. All the formed 4H‐chromenes were characterized by spectral and X‐ray methods.     

Synthesis and reactions of 3‐amino‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]‐quinazolin‐9‐one and 2‐hydrazino‐3‐phenylamino‐3H‐quinazolin‐4‐one

The reaction of 3‐N‐(2‐mercapto‐4‐oxo‐4H‐quinazolin‐3‐yl)acetamide ( 1 ) with hydrazine hydrate yielded 3‐amino‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]quinazolin‐9‐one ( 2 ). The reaction of 2 with o‐chlorobenzaldehyde and 2‐hydroxy‐naphthaldehyde gave the corresponding 3‐arylidene amino derivatives 3 and 4 , respectively. Condensation of 2 with 1‐nitroso‐2‐naphthol afforded the corresponding 3‐(2‐hydroxy‐naphthalen‐1‐yl‐diazenyl)‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]quinazolin‐9‐one ( 5 ), which on subsequent reduction by SnCl₂ and HCl gave the hydrazino derivative 6. Reaction of 2 with phenyl isothiocyanate in refluxing ethanol yielded thiourea derivative 7. Ring closure of 7 subsequently cyclized on refluxing with phencyl bromide, oxalyl dichloride and chloroacetic acid afforded the corresponding thiazolidine derivatives 8, 9 and 10 , respectively. Reaction of 2‐mercapto‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 11 ) with hydrazine hydrate afforded 2‐hydrazino‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 12 ). The reactivity 12 towards carbon disulphide, acetyl acetone and ethyl acetoacetate gave 13, 14 and 15 , respectively. Condensation of 12 with isatin afforded 2‐[N‐(2‐oxo‐1,2‐dihydroindol‐3‐ylidene)hydrazino]‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 16 ). 2‐(4‐Oxo‐3‐phenylamino‐3,4‐dihydroquinazolin‐2‐ylamino)isoindole‐1,3‐dione ( 17 ) was synthesized by the reaction of 12 with phthalic anhydride. All isolated products were confirmed by their ir, ¹H nmr, ¹³C nmr and mass spectra.     

7‐Halogenated 7‐Deazapurine 2′‐Deoxyribonucleosides Related to 2′‐Deoxyadenosine, 2′‐Deoxyxanthosine,and 2′‐Deoxyisoguanosine: Syntheses and Properties

A series of 7‐fluorinated 7‐deazapurine 2′‐deoxyribonucleosides related to 2′‐deoxyadenosine, 2′‐deoxyxanthosine, and 2′‐deoxyisoguanosine as well as intermediates 4b – 7b, 8, 9b, 10b , and 17b were synthesized. The 7‐fluoro substituent was introduced in 2,6‐dichloro‐7‐deaza‐9H‐purine ( 11a ) with Selectfluor (Scheme 1). Apart from 2,6‐dichloro‐7‐fluoro‐7‐deaza‐9H‐purine ( 11b ), the 7‐chloro compound 11c was formed as by‐product. The mixture 11b / 11c was used for the glycosylation reaction; the separation of the 7‐fluoro from the 7‐chloro compound was performed on the level of the unprotected nucleosides. Other halogen substituents were introduced with N‐halogenosuccinimides ( 11a → 11c – 11e ). Nucleobase‐anion glycosylation afforded the nucleoside intermediates 13a – 13e (Scheme 2). The 7‐fluoro‐ and the 7‐chloro‐7‐deaza‐2′‐deoxyxanthosines, 5b and 5c , respectively, were obtained from the corresponding MeO compounds 17b and 17c , or 18 (Scheme 6). The 2′‐deoxyisoguanosine derivative 4b was prepared from 2‐chloro‐7‐fluoro‐7‐deaza‐2′‐deoxyadenosine 6b via a photochemically induced nucleophilic displacement reaction (Scheme 5). The pK_a values of the halogenated nucleosides were determined (Table 3). ¹³C‐NMR Chemical‐shift dependencies of C(7), C(5), and C(8) were related to the electronegativity of the 7‐halogen substituents (Fig. 3). In aqueous solution, 7‐halogenated 2′‐deoxyribonucleosides show an approximately 70% S population (Fig. 2 and Table 1).     

Synthesis of Some Novel 2‐Anilinothiophene, 2,3′‐Bithienyl and Thienylthiopyridine Derivatives Resistance to Penicillium Digitatum Effect the Fruit

Reaction of benzotriazol‐1‐yl acetone 1 with phenyl isothiocyanate followed with α‐chloroacetone or ethyl‐α‐chloroacetate afforded 2‐anilinothiophenes 3 or 4 , respectively. Treatment of 3 with malononitrile at different reaction conditions afforded 6 or 7 . Reaction of 1 with CS₂ in DMF and phenacylbromide afforded S‐alkylated thiophene 10 . Reactions of the latter compound with different active methylene nitriles afforded thienylthiopyridine derivatives 14 and 15 . Condensation of 10 with hydrazine hydrate afforded hydrazon derivative 16 . Reaction of thiophene 17 with formamide in DMF afforded 19 which converted to N‐thienylpyrimidine 20 when treated with malononitrile. The structure of the newly synthesized compounds has been established on the basis of their analytical and spectral data. The compounds were also investigated for antibacterial and antifungal activities.     

Studies on the reaction of N‐(3‐carbethoxy‐4,5,6,7‐tetrahydrobenzo[b]thien‐2‐yl)‐N′‐phenylthiourea with hydrazine hydrate (Part 1)

The reaction of N‐(3‐carbethoxy‐4,5,6,7‐tetrahydrobenzo[b]thien‐2‐yl)‐N′‐phenylthiourea ( 1 ) with hydrazine hydrate in 1‐butanol afforded a mixture of compounds 2, 3 and 4 . Treatment of 3 and 4 with nitrous acid gave 6 and 8 respectively, while reactions of 3 with acetylacetone gave 7 . Synthesis of tetracyclic compounds 9a‐f and 11 from the reactions of 3 with ethyl orthoformate or appropriate acids, acid chloride, carbon disulphide and/or ethyl chloroformate. Also its reaction with isothiocyanate derivatives gave the corresponding thiosemicarbzides 12a,b which on, refluxing in alcoholic KOH gave the unexpected tetracyclic products 14a,b . Similarly the tetracyclic compounds 16a‐e and 19 were obtained by cyclization of 4 and 18 respectively.     

Synthesis of Some New Heterocycles Derived from Phenylacetyl Isothiocyanate

Phenylacetyl isothiocyanate (1) was reacted with benzoyl hydrazine (2a) in acetonitrile to give thiosemicarbazide derivative 3 which was cyclized by polyphosphoric acid to give 1,2,4-triazoline-5-thione derivative 4. Treatment of 1 with thiosemicarbazide (2b) yielded another 1,2,4-triazoline-5-thione derivative 5. Similar treatment of 1 with phenyl hydrazine (2c) in acetonitrile gave a differently substituted 1,2,4-triazoline-5-thione derivative 6 in one pot-reaction. On the other hand, when the reaction was carried out in acetone, a mixture of 6 and thiadiazolidine derivative 7 was obtained. However, reaction of 1 with hydrazine hydrate (2d) gave hydrazine derivative 8. Reaction of isothiocyanate 1 with anthranilic acid (9) gave benzo[d][1,3,6]oxazin-1-one derivative 10. Treatment of 1 with 2-aminothiophenol (11a), 2-aminophenol (11b) or o-phenylenediamine (11c) produced benzothiazole derivative 12a, benzoxazole derivative 12b and benzimidazole derivative 12c, respectively. The structures of all the products were confirmed by micro-analytical and spectral data.     

Synthesis of Novel Disubstituted Pyrazolo[1,5‐a]pyrimidines,Imidazo[1,2‐a]pyrimidines,and Pyrimido[1,2‐a]benzimidazoles Containing Thioether and Aryl Moieties

A series of novel 6‐[(1,3,4‐thiadiazol‐2‐yl)sulfanyl]‐7‐phenylpyrazolo[1,5‐a]pyrimidines, 5‐phenyl‐6‐[(1,3,4‐thiadiazol‐2‐yl)sulfanyl]imidazo[1,2‐a]pyrimidines, and 2‐phenyl‐3‐[(1,3,4‐thiadiazol‐2‐yl)sulfanyl]pyrimido[1,2‐a]benzimidazoles have been synthesized in four steps starting with 2‐hydroxyacetophenone. The intermediate 3‐[(1,3,4‐thiadiazol‐2‐yl)sulfanyl]‐4H‐1‐benzopyran‐4‐ones reacted with pyrazol‐3‐amines, 5‐methylpyrazol‐3‐amine, and 1H‐imidazol‐2‐amine, 1H‐benzimidazol‐2‐amine via a cyclocondensation to give the title compounds in the presence of MeONa as base, respectively. The approach affords the target compounds in acceptable‐to‐good yields. The new compounds were characterized by their IR, NMR, and HR mass spectra.     

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.     

Facile green one‐pot synthesis of novel thiazolo[3,2‐a]pyrimidine derivatives using Fe3O4@l‐arginine and their biological investigation as potent antimicrobial agents

Thiazolopyrimidine derivatives are well known because of their excellent therapeutic properties. In this investigation, an effective one‐pot three‐component method is described for the synthesis of novel 2‐[(Z )‐1‐(substituted phenyl)methylidine]‐7‐methyl‐3‐oxo‐5‐(substituted phenyl)‐2,3‐dihydro‐5H ‐thiazolo[3,2‐a]pyrimidine‐6‐carboxilic acid tert ‐butyl ester derivatives by condensation reaction of 3,4‐dihydropyrimidine‐2(1H )‐thiones, various aromatic aldehydes and chloroacetyl chloride under reflux conditions in the presence of Fe₃O₄@l ‐arginine nanoparticles as a magnetically reusable and eco‐friendly catalyst with short reaction times and moderate yields. The chemical structures of all synthesized compounds were determined using infrared, ¹H NMR and ¹³C NMR spectroscopies. In vitro antimicrobial activities of 3,4‐dihydropyrimidine‐2(1H )‐thiones and newly fused thiazolo[3,2‐a]pyrimidine derivatives were examined using the well diffusion method against diverse pathogenic strains, namely Staphylococcus aureus ATCC 6538, S. epidermidis ATCC 12228, Escherichia coli ATCC 8739 and Pseudomonas aeruginosa ATCC 9027 (bacteria), Candida albicans ATCC 10231 (yeast) and Aspergillus niger ATCC 16404 (fungus). The compounds having 2‐hydroxy, 4‐hydroxy, 2‐chloro and 4‐chloro groups attached to the phenyl ring on the pyrimidine and 4‐CH₃, 4‐OCH₃ and 3‐NO₂ groups attached to benzylidine on the thiazolo moiety showed significant antibacterial activity.     

Synthesis of New Fused and Spiro Heterocyclic Systems from 3,5‐Pyrazolidinediones

4‐Bromo‐1‐phenyl‐3,5‐pyrazolidinedione 2 reacted with different nucleophilic reagents to give the corresponding 4‐substituted derivatives 3–8 . The cyclized compounds 9–11 were achieved on refluxing compounds 3 , 4 or 6_a in glacial acetic acid or diphenyl ether. 4,4‐Dibromo‐1‐phenyl‐3,5‐pyrazolidinedione 12 reacted with the proper bidentates to give the corresponding spiro 3,5‐pyrazolidinediones 13–15 , respectively. The 4‐aralkylidine derivatives 16_a‐c , were subjected to Mannich reaction to give Mannich bases 17_a‐c‐22_a‐c , respectively. 4‐(p‐Methylphenylaminomethylidine)‐1‐phenyl‐3,5‐pyrazolidinedione 23 or 4‐(p‐methylphenylazo)‐1‐phenyl‐3,5‐pyrazolidinedione 29 were prepared and reacted with active nitriles, cyclic ketones and N,S‐acetals to give pyrano[2,3‐c]pyrazole, pyrazolo[4′,3′:5,6]pyrano[2,3‐c]pyrazole, spiropyrazole‐4,3′‐pyrazole and spiropyrazole‐4,3′‐[1,2,4]triazolane derivatives 24–34 , respectively.     

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)     

An Alternating Copolymer Derived from Indolo[3,2‐b]carbazole and 4,7‐Di(thieno[3,2‐b]thien‐2‐yl)‐2,1,3‐benzothiadiazole for Photovoltaic Cells

An alternating narrow bandgap conjugated copolymer (PICZ‐DTBT, E_g = 1.83 eV) derived from 5,11‐di(9‐heptadecanyl)indolo[3,2‐b]carbazole and 4,7‐di(thieno[3,2‐b]thien‐2‐yl)‐2,1,3‐benzothiadiazole (DTBT), was prepared by the palladium‐catalyzed Suzuki coupling reaction. The resultant polymer absorbs light from 350–690 nm, exhibits two absorbance peaks at around 420 and 570 nm and has good solution processibility and thermal stability. The highest occupied molecular orbital (HOMO) energy level and lowest unoccupied molecular orbital (LUMO) level of the copolymer determined by cyclic voltammetry were about −5.18 and −3.35 eV, respectively. Prototype bulk heterojunction photovoltaic cells from solid‐state composite films based on PICZ‐DTBT and [6,6]‐phenyl‐C₇₁ butyric acid methyl ester (PC₇₁BM), show power conversion efficiencies up to 2.4% under 80 mW · cm⁻² illumination (AM1.5) with an open‐circuit voltage of V_oc = 0.75 V, a short current density of J_sc = 6.02 mA · cm⁻², and a fill factor of 42%. This indicates that the copolymer PICZ‐DTBT is a viable electron donor material for polymeric solar cells.

     

Regioselective Synthesis of the 5,6‐Dihydro‐4H‐furo[2,3‐c]pyrrol‐4‐one Skeleton: A New Class of Compounds

We hereby report the first preparation of the 5,6‐dihydro‐4H‐furo[2,3‐c]pyrrol‐4‐one ( 3 ) and its derivatives starting from methyl 3‐(methoxycarbonyl)furan‐2‐acetate ( 8 ). The ester functionality connected to the methylene group was regiospecifically converted to the desired monohydrazide 9 . Conversion of 9 into the acyl azide 10 followed by Curtius rearrangement gave the corresponding isocyanate derivative 11 (Scheme 2). Reaction of 11 with different nucleophiles produced urethane and urea derivatives (Scheme 3). Intramolecular cyclization reactions provided the target compounds (Scheme 5). Removal of the amine‐protecting group formed the title compound 3 .     

Microwave Induced Synthesis of 3‐Aryl‐6‐(6‐/8‐substituted 4‐chloroquinoline‐3‐yl) ‐ s ‐triazolo [3,4‐b] −1,3,4‐thiadiazoles

The condensation of 4‐amino‐3‐aryl‐5‐mercapto‐1, 2, 4‐triazoles (1a‐f) with 6‐/8‐substituted 1,4‐dihydro‐4‐oxo‐quinoline‐3‐carboxylic adds (2a‐d) in the presence of phosphorus oxychloride on refluxng or under microwave irradiation gave twenty four novel 3‐aryl‐6‐ (6‐/8‐substituted 4‐chloroquinoline‐3‐yl)‐s‐triazolo[3,4‐b]‐1, 3,4‐thiadiazoles (4a‐x), Considerable increase in the reaction rate has been observed with improved yields under microwave irradiation. The structures of the compounds synthesized were determined by elemental analyses, IR, ¹H NMR and MS spectra. Their spectral properties and the reaction mechanism were also discussed. The preliminary biological test showed that some of compounds bad moderate antibacterial activities.     

Reaction of 2‐Phenyl‐4‐arylidene‐1,3‐oxazolones with Different Nucleophiles for Synthesis of Some New Heterocycles

Refluxing of 1,3‐oxazolone ( 1a ) with malononitrile in dry benzene and in the presence of ammonium acetate afforded imidazolone derivative ( 2 ). However, carrying out the same reaction in absolute ethanol and in the presence of piperidine as a base gave the benzamide derivative ( 4 ). Fusion of ( 1a ) with p‐anisidine gave the open adduct benzamide ( 6 ), which cyclized in acidic medium to give imidazolone derivative ( 7 ). Heating of imidazolone ( 7 ) with malononitrile above its melting point afforded 1,3‐diazepine derivative ( 8 ). Reaction of the carbohydrazide ( 9 ) with isatin in ethanol gives the corresponding Schiff base ( 11 ), which then reacted with acetyl acetone, ethyl acetoacetate, ethyl cyanoacetate, and malononitrile in n‐butanol and piperidine to afford benzamide derivative ( 13 , 14 , 15 ) and ( 16 ), respectively. The structures of the newly synthesized compounds were established on the basis of IR, ¹H‐NMR, mass spectra, and elemental analyses.     

Synthesis of some novel pyrazolo[1,5-a]quinazolines and their fused derivatives

New pyrazolo[1,5-a]quinazoline-3-carbonitriles 4a,b were obtained via cyclocondensation of 5-amino-3-cyanomethyl-1H-pyrazole-4-carbonitrile (1) with enaminones of 1,3-cyclohexanedione derivatives 2a,b in refluxing glacial acetic acid. Condensation of compounds 4a,b with various aromatic aldehydes furnished the corresponding arylidene derivatives 6a–j. On the other hand, condensation of 4a,b with o-hydroxybenzaldehydes yielded the polyheterocyclic compounds 10a–h. Coupling of compounds 4a,b with aryldiazonium chlorides led to formation of 2-arylhydrazono derivatives 12a–h. Also, reaction of compounds 4a,b with phenyl isothiocyanate, followed by addition of ethyl chloroacetate and chloroacetonitrile, afforded the polyheterocyclic compounds based on pyrazolo[1,5-a]quinazoline core. The reaction of compounds 4a,b with phenyl isothiocyanate and elemental sulfur gave the thiazole-2-thione derivatives 25a,b. The reaction of enamines of compounds 4a,b with each of hydrazine hydrate and guanidine hydrochloride afforded pyrazolo[4″,3″:5′,6′]pyrido[4′,3′:3,4]pyrazolo[1,5-a]quinazolin-8-ones 30a,b and pyrimido[5″,4″:5′,6′]pyrido[4′,3′:3,4]pyrazolo[1,5-a]quinazolin-9(10H)-ones 33a,b, respectively. The structures of all the newly synthesized compounds were elucidated by elemental analyses and spectral data. The plausible mechanisms have been postulated to account for their formation.     

Reactivity of (2‐methylsulfanyl‐4‐oxo‐6‐phenyl‐4h‐pyrimidin‐3‐yl)‐acetic acid methyl ester towards hydrazine hydrate and benzylamine

The title ester 1 reacted with hydrazine hydrate to give hydrazide 2 , which underwent intramolecular cyclization to yield 1‐amino‐7‐phenyl‐1H‐imidazo[1,2‐a]pyrimidine‐2,5‐dione ( 3 ) or took place in a substitution reaction with benzylamine to form N‐benzyl‐2‐(2‐benzylamino‐4‐oxo‐6‐phenyl‐4H‐pyrimidin‐3‐yl)‐acetamide ( 4 ). The reaction of ester 1 with benzylamine gave corresponding amide 7 , disubstituted derivative 4 or 1‐benzyl‐7‐phenyl‐1H‐imidazo[1,2‐a]pyrimidine‐2,5‐dione ( 8 ) depending on the reaction conditions.     

Synthesis of Pyrazolo[1,5‐a][1,3,5]triazine,Pyrazolo[1,5‐a]pyrimidine,and Imidazo[1,2‐b]pyrazole Derivatives Based on Imidazo[2,1‐b]thiazole Moiety

3(5)‐Aminopyrazole derivative ( 6 ) has been synthesized by the reactions of the versatile unreported 2‐cyano‐N ′‐(1‐(3‐methyl‐6‐phenylimidazo[2,1‐b ]thiazol‐2‐yl)ethylidene)acetohydrazide ( 3 ) with phenyl isothiocyanate in KOH/DMF solution followed by reaction with methyl iodide and hydrazine hydrate. Reaction of compound 6 with some 1,3‐dicarbonyl compounds yielded pyrazolo[1,5‐a ]pyrimidine derivatives ( 14 – 17 ). Alkylation of compound 6 with various halo reagents, followed by intramolecular cyclization, yielded the corresponding imidazo[1,2‐b ]pyrazole derivatives 27 , 29 , 31 , and 33 . All newly synthesized compounds were elucidated by considering the data of both elemental analysis and spectral data.