Design,synthesis, and biological evaluation of novel substituted imidazo[2,1-a]isoindole derivatives as antibacterial agents

An efficient protocol has been developed for the synthesis of fused imidazo[2,1-a]isoindol-5-ones (2a–d) from 2-iodo benzoic acids and N,N-carbonyldiimidazole (CDI) using one-pot Pd-catalyzed C?C bond coupling. The reaction of imidazo[2,1-a]isoindol-5-one (2a–d) with substituted α-bromo ketones in toluene afforded corresponding imidazo[2,1-a]isoindolium derivatives (3a–i) in good yields. The structures of the title compounds were well established on the basis of infrared (IR), ¹H NMR, carbon-13 nuclear magnetic resonance (¹³C NMR), mass spectral data, and elemental analysis (C, H, and N). In vitro antibacterial results revealed that, the compounds 3b and 3i were found to possess an excellent broad spectrum of inhibiting potency against all the tested bacterial strains with minimum inhibitory concentration values ranging from 3.125 to 25?µg mL^?1.     

Synthesis of Fused Tetrazolo[1,5‐c] pyrrolo[3,2‐e]pyrimidines and Their Reductive Conversion to New 4‐Aminopyrrolo[2,3‐d]pyrimidines

Some new 7,9‐substituted 7H‐1,2,3,4‐tetrazolo[1,5‐c]pyrrolo[3,2‐e]pyrimidines 5 have been synthesized either by diazotization of 4‐hydrazino‐5,7‐disubstituted‐7H‐pyrrolo[2,3‐d]pyrimidines 4 obtained by hydrazinolysis of 4‐chloro‐5,7‐disubstituted 7H‐pyrrolo[2,3‐d]pyrimidines 3 or via a substitution reaction between 3 and sodium azide. 5,7‐Disubstituted‐7H‐pyrrolo[2,3‐d]pyrimidin‐4(3H)‐ones 2 were obtained by cyclocondensation of 1,4‐disubstituted 2‐amino‐3‐cyanopyrroles 1 with formic acid, which, on chlorination using phosphorus oxychloride, afforded 3. 2‐Amino‐3‐cyanopyrroles 1 were synthesized from the reaction between (2-bromo-1-(4-fluorophenyl) ethylidene) propanedinitrile and substituted aromatic amines under Gewald reaction conditions. A novel route for the synthesis of 4‐amino‐5,7‐disubstituted‐7H‐pyrrolo[2,3‐d]pyrimidines 6 by the reductive ring cleavage of 5 has been reported.     

A new approach to the synthesis of pyridazino[4,5-c]pyridazinones

The reaction of 5-hydrazinopyridazin-3(2H)-ones 1 with α-keto diester 2 in acetic acid afforded the corresponding 4,6-dihydropyridazino[4,5-c]pyridazin-5(1H)-ones 3 and pyrrolo[2,3-d)pyridazin-4(5H)-ones 4 . Compounds 3 were also obtained from 4-bromo-5-hydrazinopyridazin-3(2H)-ones 8 and 2 under milder conditions. 5-Bromo-4-hydrazinopyridazin-3(2H)-one 9 , the regioisomer of 8b , also reacted readily with 2a to give 4,7-dihydropyridazino[4,5-c]pyridazin-8(1H)-one 10b , the regioisomer of 3b .     

Synthesis of some novel 5-substituted benzamido-6-arylamino-pyrazolo[3,4-D]pyrimidin-4-one derivatives for herbicidal activity

Abstract

Sixteen novel 3-methylthio-5-substituted benzamido-6-arylamino-1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4 (5H)-one derivatives (4a–p) were successfully synthesized from iminophosphoranes, aryl isocyanate, and substituted benzoylhydrazine. The structures of the title compounds were elucidated by FT-IR, ¹H NMR, ¹³C NMR, and HRMS. Herbicidal activity of the compounds 4a–p against Brassica napus (rape), Echinochloa crusgalli (barnyard grass), Cucumis sativus (cucumber), and Triticum aestivum (wheat) were determined. The results showed that 5-(2-chlorobenzamido)-6-phenylamino-3-methylthio-1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4 (5H)-one (4c) displayed remarkable inhibition activity against the stalk and root of rape with 100% inhibition rate at the dosages of 10?mg/L and 100?mg/L, and 5-(4-nitrobenzamido)-6-phenylamino-3-methylthio-1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4 (5H) -one (4d) exhibited excellent activity against the stalk and root of barnyard grass with 100% inhibition rate at the same dosages.     

Water-Mediated Selective Synthesis of Pyrazolo[1,5-a]quinazolin-5(4H)-ones and [1,2,4]Triazolo[1,5-a]quinazolin-5(4H)-one via Copper-Catalyzed Cascade Reactions

A convenient and sustainable synthesis of pyrazolo[1,5-a]quinazolin-5(4H)-ones and [1,2,4]triazolo[1,5-a]quinazolin-5(4H)-one through copper-catalyzed cascade reactions of 2-bromobenzoates with 1H-pyrazol-5-amines or 1H-1,2,4-triazol-5-amine under ligand-free conditions in water is presented. It is notable that aqueous medium turned out to be crucial for the chemoselective formation of the title compounds. Compared with literature protocols, this new method showed advantages such as simple and sustainable procedure, commercially available starting materials, and convenient reuse of the reaction medium together with the copper catalyst.     

Facile Synthesis of 2-Alkylthio-5,6,7,8-tetrahydrobenzothieno[2,3-d]pyrimidin-4(3H)-ones

Isothiocyanate 2, obtained from aza-Wittig reaction of iminophosphorane 1 with CS₂, reacted with amine to give 2-thioxo-2,3,5,6,7,8-hexahydrobenzothieno[2,3-d]pyrimidin-4(1H)-ones 4 in the presence of sodium ethoxide. S-Alkylation of 4 produced 2-alkylthio-5,6,7,8-tetrahydrobenzothieno[2,3-d]pyrimidin-4(3H)-ones 5 in good yields.     

Synthesis of oxazole and furan derivatives via Rh2(OAc)4-catalyzed C≡X bond insertion of cyclic 2-diazo-1,3-diketones with nitriles and arylacetylenes

Abstract

A convenient and efficient procedure for the synthesis of 2-substituted-6,7-dihydrobenzo[d]oxazol-4(5H)-ones and 2-aryl-6,7-dihydrobenzofuran-4(5H)-ones through a Rh₂(OAc)₄-catalyzed C≡X (X?=?N, C) insertion of cyclic 2-diazo-1,3-diketones with nitriles and aromatic alkynes has been developed. This reaction uses readily available starting materials and stable cyclic 2-diazo-1,3-diketone compounds, with desired products formed in good to high yields. A tentative mechanism involving a C≡X bond insertion and 1,5-dipolar electrocyclization/ring opening and cyclization sequence for this reaction is proposed.     

Synthesis and antimicrobial activity of new derivatives of pyrano[4',3':4',5']pyrido[3',2':4,5]thieno[3,2-d]pyrimidine and new heterocyclic systems

Taking into account previously obtained biological results on some polyheterocyclic compounds (containing different heteroatoms) and in particular on several 8-amino-5-isopropyl-2,2-dimethyl-10-(methylthio)-1,4-dihydro-2H-pyrano[4’’,3’’:4’,5’]pyrido[3’,2’:4,5]thieno[3,2-d]pyrimidines Ia-v we have carried out the synthesis of twentyone 8-amino-5-isobutyl-2,2-dimethyl-10-(methylthio)-1,4-dihydro-2H-pyrano[4’’,3’’:4’,5’]pyrido[3’,2’:4,5]thieno[3,2-d]pyrimidines 6. Therefore we have slightly modified the structure of the previously studied I introducing at C-5 an isobutyl group instead of the previously examined isopropyl ones in order to see if this variation (changing a little the lipophilicity) will affect the biological activity. Furthermore thieno[3,2-d]pyrimidine-8-thione 7 and their S-alkylated 8 were synthesized. Finally by alkylation of 5-isobutyl-2,2-dimethyl-10-thioxo-1,4,10,11-tetrahydro-2H-pyrano[4'',3'':4',5']pyrido[3',2':4,5]thieno[3,2-d]pyrimidin-8(9H)-one 3 with alkyl dichlorides (bifunctional reagents) we realized the cyclization of a thiazole or thiazine ring on the [b] side of the pyrimidine ring with formation of the new condensed pentaheterocyclic systems: pyrano[4'',3'':4',5']pyrido[3',2':4,5]thieno[3,2-d][1,3]thiazolo[3,2-a]pyrimidin-8-one 11 and pyrano[4''',3''':4'',5'']pyrido[3'',2'':4',5']thieno[3',2':4,5]pyrimido[2,1-b][1,3]thiazin-8-one 12. It was found that some of the synthesized compounds showed interesting antimicrobial activity (by agar diffusion method) against some gram-positive and gram-negative bacilli strains.     

Synthesis and in vitro anticancer activity of pyrazolo[1,5-a]pyrimidines and pyrazolo[3,4-d][1,2,3]triazines

A novel series of pyrazolo[1,5-a]pyrimidines 14a–j and pyrazolo[1,5-a]quinazolines 18a, b were synthesized via condensation of 5-amino-1H-pyrazoles 10a, b with 3-(dimethylamino)-1-aryl-prop-2-en-1-ones 11a–e and 2-((dimethylamino)methylene)-5,5-dimethylcyclohexane-1,3-dione (15), respectively, in glacial acetic acid. Finally, treatment of 10a, b with sodium nitrite (NaNO₂) afforded pyrazolo[3,4-d]triazines 20a, b. Structures of compounds were confirmed by their spectral data. These compounds were screened for their in vitro cytotoxic activities against human cancer cell lines (HepG-2 and MCF-7) using 3-[4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The results reveal that, the compounds 14b and 14h were the most potent in comparison with doxorubicin. The structure–activity relationship was discussed.     

On the condensation of 2,2-difluoro-4-methyl-benzo[d]-1,3,2-dioxaborines with cyano acetic acid derivatives. Formation and transformation of 3-cyano-4-methyl-benzo[b]pyran-2-ones and their 2-imine precursors

Summary By condensation of 2,2-difluoro-4-methyl-benzo[d]-1,3,2-2H-dioxaborines (12) with cyano acetic acid derivatives in presence of weak bases, 3-cyano-4-methyl-benzo[b]pyran-2-ones (13) or their 3-cyano-4-methyl-benzo[b]pyran-2-imine precursors (14) are available in satisfactory yields.

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Zur Kondensation von 2,2-Difluor-4-methyl-benzo[d]-1,3,2-2H-dioxaborinen mit Cyanessigsäure- Derivaten. Bildung und Umwandlung von 3-Cyano-4-methyl-benzo[b]pyran-2-onen und ihrer 2-Imino-Vorstufen

Zusammenfassung Durch Kondensation von 2,2-Difluor-4-methyl-benzo[d]-1,3,2-2H-dioxaborinen (12) mit Cyanessigsäure-Derivaten in Gegenwart von Hilfsbasen entstehen in befriedigenden Ausbeuten 3-Cyan-4-methyl-benzo[b]pyran-2-one (13) oder ihre 3-Cyan-4-methyl-benzo[b]pyran-2-imino-Vorstufen (14).

     

Efficient synthesis and characterization of novel bis-heterocyclic derivatives and benzo-fused macrocycles containing oxazolone or imidazolone subunits

Bis(3-(arylthiomethyl)benzaldehydes), linked to aliphatic spacers via ethers, were prepared and used as key synthons for the bis(2-phenyloxazol-5(4H)-ones) via their reaction with benzoylglycine in acetic anhydride in the presence of fused sodium acetate at 100°C for 6 hours. Bis(oxazol-5(4H)-ones) were reacted with the appropriate aromatic or heterocyclic amines in glacial acetic acid in the presence of fused sodium acetate at 100°C for 24 hours to afford a novel series of bis(2-phenylimidazol-4-ones) and their related hybrids with benzo[d]thiazole and pyrimidine-2,4(1H,3H)-dione. Moreover, bis(oxazol-5(4H)-ones) reacted with (4-aminobenzoyl)glycine to afford bis[(4-(5-oxo-1H-imidazol-1-yl)benzoyl)glycine] derivatives followed by their reaction with anisaldehyde in acetic anhydride containing fused sodium acetate at 100°C for 12 hours to afford bis(5-oxo-1H-imidazol-1-yloxazol-5(4H)-one) hybrids. Furthermore, bis(3-(arylthiomethyl)benzaldehydes) were reacted with 2,2′-(terephthaloylbis(azanediyl))diacetic acid in acetic anhydride containing fused sodium acetate at 100°C for 12 hours to give benzo-fused macrocycles containing oxazolone subunits which reacted with appropriate aromatic amines in DMF and glacial acetic acid containing fused sodium acetate at 100°C for 24 hours to give benzo-fused macrocycles containing imidazolone subunits.     

Synthesis and reactions of halo-, nitro-, and arylazo-substituted 3-aminotropolones. Formation of 8H-cyclohept[d]oxazol-8-one derivatives

3-Acetamidotropolone ( 1a ) reacted with bromine and fuming nitric acid to afford respectively 3-acetamido-7-bromo- ( 1b ) and -5,7-dibromotropolone ( 1c ) and 3-acetamido-5-nitrotropolone ( 1d ). Azo-coupling reaction of 1a gave 3-acetamido-5-(4-methylphenylazo)tropolone ( 1f ). Bromination of 1d and 1f gave 7-bromo-substituted compounds 1e and 1g , respectively. The compounds 1b-g were hydrolyzed to afford 3-aminotropolones 4b-g , which reacted with triethyl orthoformate to give the corresponding 8H-cyclohept[d]oxazol-8-ones 5b-g . Heating of 3-acetamidotropolones 1a-d with polyphosphoric acid gave 2-methyl-8H-cyclohept[d]oxazol-8-ones 6a-d .     

Synthesis and antimicrobial activity of some 2-alkyl-2H-1,4-benzothiazin-3(4H)-ones and 2-alkylbenzo[d]imidazolo[2,1-b]-thiazolidin-3-ones

Summary Sodium 2-aminothiophenoxide (1) reacts with ethyl 2-bromoalkanoates (2) under direct cyclization to form 2-alkyl-2H-1,4-benzothiazin-3(4H)-ones (3). Reaction of the sodium salt of 2-mercaptobenzimidazole (4) with2 or 2-bromoalkanoic acids (5) affords only S-alkylated products (6 or7, respectively). The cyclization products — 2-alkylbenzo[d]imidazolo[2,1-b]thiazolidin-3-ones (8) — can be obtained only from the corresponding 2-(2-benzimidazolylthio)alkanoic acids (7) by the action of acetic anhydride. Both compounds3 and8 exhibit only moderate antimicrobial activity against some gram-positive bacteria.

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Synthese und antimikrobielle Wirkung von einigen 2-Alkyl-2H-1,4-benzothiazin-3(4H)-onen und 2-Alkylbenzo[d]imidazolo[2,1-b]thiazolidin-3-onen

Zusammenfassung Bei der Reaktion von Natrium-2-aminothiophenolat mit 2-Bromoalkansäure-ethylestern (2) entstehen als Cyclisierungsprodukte 2-Alkyl-2H-1,4-benzothiazin-3(4H)-one (3). Die Umsetzung von Natriumbenzimidazol-2-thiolat mit2 oder mit 2-Bromoalkansäuren (5) liefert nur S-Alkylierungsprodukte (6 oder7). Die Cyclisierungsprodukte — 2-Alkylbenzo[d]imidazolo[2,1-b]thiazolidin-3-one (8) — sind nur durch Umsetzung von entsprechenden 2-(2-Benzimidazolylthio)-alkansäuren (7) mit Acetanhydrid erhältlich. Die Verbindungen3 und8 weisen nur mäßige antimikrobielle Wirkung gegen einige gram-positive Bakterien aus.

     

Synthesis of Precursors of Heterocyclic cis-β-Amino Alcohols by Intramolecular Amidoalkylation of 4-Hydroxyoxazolidin-2-ones

The reaction of intramolecular amidoalkylation of 4-hydroxyoxazolidin-2-ones leads to formation of novel and rare heterocyclic systems: substituted 1,5,6,10b-tetrahydro[1,3]oxazolo[4,3-a]isoquinolin-3-ones, 3a,4,5,10b-tetrahydro[1,3]dioxolo[4',5':6,7]naphtho[1,2-d][1,3]oxazol-2(1H)-ones, and 5,6,10,10a-tetrahydro-1H-di[1,3]oxazolo[3,4-d:4,3-g][1,4]diazepine-3,8-diones. Mild reaction conditions and the simplicity of isolation of the compounds formed make it possible to obtain the indicated heterocycles in high yields.     

SYNTHESIS OF 15H-ISOQUINO[2′,3′:3,4]IMIDAZO[2,1-B]QUINAZOLINE-7,13,15-TRIONES AND 14H-ISOQUINO[2′,3′:3,4]IMIDAZO[2,1-B]BENZO[G]QUINAZOLINE-8,14,16-TRIONE AS NEW POLYCYCLIC FUSED-RING SYSTEMS

3-Thioxo-2H-imidazo[1,5-b]isoquinoline-1,5-dione (3) and 2-sub-stituted 3-thioxo-2H-imidazo[1,5-b]isoquinoline-1,5-diones (4a–l) were prepared from the reaction of 2-thiohydantoin (2) and 3-substituted 2-thiohydantoin (5a–l) with 2-formyl benzoic acid (1). Alkylation of 3 under an anhydrous basic conditions afforded 4a–i. The alkylation of 3 in aqueous basic solution afforded 3-(alkylmercapto)imidazo[1,5-b]isoquinoline-1,5-diones (7a,b). Reactions of the aromatic amino acids 9a,b and 12 with 7a afforded 2-(2H-1,5 dioxoimidazo[1,5-b]isoquinazolin-3-ylideneamino)benzoic acids (10a, b) and 3-(2H-1,5-dioxoimidazo[1,5-b]isoquinazolin-3-ylideneamino)2-naphthalenecarboxylic acid (13), which were then cyclyzed by heating in acetic anhydride to afford 15H-isoquino[2′,3′ :3,4] imidazo[2,1-b]quinazoline-7,13,15-triones (11a,b) and 14H-isoquino[2′,3′:3,4]imidazo[2,1-b]benzo[g]quinazoline-8,14,16-trione (14). Some of the new compounds were tested for their antitumor activities.     

One‐pot Combinatorial Synthesis of Benzo[4,5]imidazo‐[1,2‐a]thiopyrano[3,4‐d]pyrimidin‐4(3H)‐one Derivatives

A series of novel fused tetracyclic benzo[4,5]imidazo[1,2‐a]thiopyrano[3,4‐d]pyrimidin‐4(3H)‐one derivatives were synthesized via the reaction of aryl aldehyde, 2H‐thiopyran‐3,5(4H,6H)‐dione, and 1H‐benzo[d]imidazol‐2‐amine in glacial acetic acid. This protocol features mild reaction conditions, high yields and short reaction time.     

Design,synthesis, and toward a side-ring optimization of tricyclic thieno[2,3-d]pyrimidin-4(3H)-ones and their effect on melanin synthesis in murine B16 cells

Abstract

Herein, we report the synthesis of 48 novel 3-sulfonylamides containing a tricyclic thieno[2,3-d]pyrimidin-4(3H)-one moiety, and their influence on melanin synthesis in murine B16 cells. All target sulfonylamides were synthesized through key intermediate 3-nitro-thieno[2,3-d]pyrimidin-4(3H)-ones using three types of ipso-nitration reactions. In this case, we converted the pyrido[1,2-a]- fragment of the thieno[2,3-d]pyrimidine moiety to pyrrolo[1,2-a]- and azepino[1,2-a]- side-rings in order to evaluate the bioactivities of the synthesized derivatives for a structure activity-relationships point of view. The obtained results suggest that some of the selected compounds revealed a promising influence on melanin synthesis in murine B16 cells and may serve as lead compounds for further drug discovery and development.     

Novel Selected Tandem Transformations of the Amino and Carbonyl/Nitrile Groups in the Gewald Thiophenes

Novel transformations of the amino and carbonyl/nitrile groups in the Gewald thiophenes were studied for thienopyrimidine synthesis. It was found that 2-amino-thiophene-3-carboxamides and ethyl 2-(acetylamino)-4,5,6,7-tetrahydro-1-benzothiophene-3-carbo- xylate did not yield tetrazole derivatives, neither in the reaction with triethyl orthoformate and sodium azide, nor in the reaction with phosphorus oxychloride and sodium azide, correspondingly. On the contrary, derivatives of thieno[2,3-d]pyrimidin-4(3H)-one and thieno[2,3-d][1,3]oxazin-4-one were isolated. New 2-azidothiophenes [2-azido-4,5,6,7-tetra hydro-1-benzothiophene-3-carbonitrile and 2-azido-4,5,6,7-tetrahydro-1-benzothiophen-3-yl(phenyl)methanone] were synthesized and used in anionic domino reactions with activated acetonitriles to yield thieno[3,2-e][1,2,3]triazolo[1,5-a]pyrimidines and/or 2-(5-amino-1H-1,2,3-triazol-1-yl)thiophenes. Finally, a new ring system of thieno[3,2-e]pyrazolo[1,5-a]pyrimidine was synthesized via a domino reaction of ethyl 2-[(2Z)-2-(1-chloro-2-ethoxy-2-oxoethylidene)hydrazino]-4,5,6,7-tetrahydro-1-benzothiophene-3-carboxylate with activated acetonitriles.     

Facile synthesis and characterization of novel pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-one and pyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidine incorporating 1,3-diarylpyrazole moiety

4-(3-(4-Hydroxyphenyl)-1-phenyl-1H-pyrazol-4-yl)-6-phenyl-2-thioxo-1,2-di hydro-pyridine-3-carbonitrile (1) reacted with ethyl chloroacetate (2) in ethanolic sodium acetate solution to yield the corresponding ethyl (3-cyanopyridin-2-ylsulphanyl)acetate derivative 3. Intramolecular cyclization of compound 3 was achieved by its heating in DMF containing potassium carbonate to afford the corresponding ethyl 3-aminothieno[2,3-b]pyridine-2-carboxylate derivative 4 which reacted with hydrazine hydrate in refluxing pyridine to yield the starting material 3-aminothieno[2,3-b]pyridine-2-carbohydrazide derivative 7. Compound 7 reacted with different reagents such as triethylorthoformate, formic acid, acetic acid and acetic anhydride to afford the target molecules pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-one derivatives 8–10, 12 and 13 in good to excellent yields. On the other hand, pyridine-2(1H)-thione derivative 1 reacted with hydrazine hydrate in refluxing pyridine to give the other starting material 3-amino-1H-pyrazolo[3,4-b]pyridine derivative 20 which reacted with acetylacetone under reflux to afford the target molecule pyrido[2′,3′:3,4]pyrazolo[1,5-a]-pyrimidine derivative 21 in a good yield. The structures of target molecules were elucidated using elemental analyses and spectral data.     

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.