Naturstoffchemie, 174. Mitt. [1]: Oxidation von Acronycin mit Kaliumpermanganat

Zusammenfassung Die Oxidation des Acridonalkaloids Acronycin (1) mit Kaliumpermanganat führt zu (1S-cis)-1,2,3,12-Tetrahydro-1,2-dihydroxy-6-methoxy-3,3,12-trimethyl-7-H-pyrano[2,3-c]acridin-7-on (2), 1-Hydroxy-6-methoxy-3,3,12-trimethyl-1H-pyrano[2,3-c]acridin-2,7(3H,12H)-dion (3) und 1-Hydroxy-6-methoxy-3,3,12-trimethyl-1-(2-oxopropyl)-1H-pyrano[2,3-c]acridin-2,7(3H,12H)-dion (4).

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Natural product chemistry, part. 174 [1]: Oxidation of acronycine by potassium permanganate

Summary Oxidation of the acridone alkaloid acronycine (1) by potassium permanganate results in oxidation of the cromenering to give (1S-cis)-1,2,3,12-tetrahydro-1,2-dihydroxy-6-methoxy-3,3,12-trimethyl-7H-pyrano[2,3-c]acridine-7-one (2), 1-hydroxy-6-methoxy-3,3,12-trimethyl-1H-pyrano-[2,3-c]acridine-2,7(3H,12H)-dione (3) and 1-hydroxy-6-methoxy-3,3,12-trimethyl-1-(2-oxopropyl)-1H-pyrano[2,3-c]acridine-2,7(3H,12H)-dione (4).

     

A Convenient Synthesis for Some New Pyrido[4′,3′:4,5]thieno[2,3-d]pyrimidines and Related Fused 1,2,4-Triazolo and 1,3,4-Thiadiazolo-derivatives

Diethyl 2-isothiocyanato-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3,6 dicarboxylate 1 is a convenient and useful starting matrial for the constructions of heterocyclic systems. It was utilized to synthesize derivatives of the novel heterocyclic systems pyrido[4',3':4,5]thieno[2,3-d]pyrimidine 4 , 10 , pyrido[4',3':4,5]thieno[2,3-d]-[1,2,4]triazolo[1,5-a]pyrimidine 7 , 11a-e and pyrido[4',3':4,5]thieno[2,3-d][1,3,4]thiadiazolo[3,2-a]pyrimidine 12-14 .     

Reactions with pyrrolidine-2,4-diones,I. New synthesis of pyrano[2,3-c]pyrrole and pyrrolo[3,4-b]pyridine systems

The synthesis of some substituted 4-hydroxy-2,5,6,7-tetrahydro-pyrano[2,3-c]pyrrole-2,5-diones (5) and 4-hydroxy-1,2,6,7-tetrahydro-5H-pyrrolo[3,4-b]pyridine-2,5-diones (6) by reacting 1,5-diaryl-pyrrolidine-2,4-diones (1) and 1,5-diaryl-1,5-dihydro-4-amino-2H-pyrrol-2-ones (3) with bis-2,4,6-trichlorophenyl malonates (4) is described.Dedicated to Prof. Dr. Dr. h. c.O. Kratky, Graz, on the occasion of his 80th birthday.     

Synthesis of 3-Substituted Pyrido[4′,3′:4,5]thieno[2,3-d]pyrimidines and Related Fused Thiazolo Derivatives

New ethyl 3-(substituted)-4-oxo-2-thioxo-1,2,3,4,5,6,7,8-octahydropyrido[4',3':4,5]thieno-[2,3-d]pyrimidine-7-carboxylates ( 3a , b ), ( 6 ),( 11-13 ), ethyl 3-methyl-5-oxo-2,3,6,9-tetrahydro 5 H -pyrido[4',3':4,5]thieno[2,3-d][1,3]thiazolo[3,2-a]pyrimidine-8(7H)-carboxylate ( 4 ), and ethyl 2-methyl-5-oxo-2,3,6,9-tetrahydro-5 H -pyrido[4',3':4,5]thieno[2,3-d][1,3]thiazolo[3,2-a]-pyrimidine-8(7H)-carboxylate ( 8 ) have been synthesized from diethyl 2-isothiocyanato-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3,6-dicarboxylate 1. The structure of these compounds as well as their intermediates have been established by their spectral data.     

SYNTHESIS AND REACTIONS OF SOME NEW HETEROCYCLIC COMPOUNDS CONTAINING THE THIENYLTHIENO[2,3-B]PYRIDINE MOIETY

(4-Aryl-3-cyano-6-(2-thienyl)pyridin-2-ylthio)acethydrazides (5a–c), 3-amino-4-aryl-6-(2-thienyl)thieno[2,3-b]pyridine-2-carbohydrazides (6a–c) and 3-amino-4-phenyl-6-(2-thienyl)thieno[2,3-b]pyridine-2-carboxylic acid (30) were prepared and employed as key intermediates in the synthesis of the title compounds.     

Synthesis and pharmacological evaluation of 5-[2′-(1H-tetrazol-5-yl)-biphenyl-4-ylmethyl]-4,5,6,7-tetrahydro-thieno[3,2-c]pyridine derivatives as platelet aggregation inhibitors

One pot synthesis and characterization of new 5-[2′-(1H-tetrazol-5-yl)-biphenyl-4-ylmethyl]-4,5,6,7-tetrahydro-thieno[3,2-c]pyridines (3a–k) using amides (2a–k) were reported. The prepared 5-[2′-(1H-tetrazol-5-yl)-biphenyl-4-ylmethyl]-4,5,6,7-tetrahydro-thieno[3,2-c]pyridine (3a) is a bioisostere of 4′-(6,7-dihydro-4H-thieno [3,2-c]pyridin-5-ylmethyl)-biphenyl-2-carboxylic acid (1), having good in vivo antithrombotic activity compared with Clopidogrel. The new tetrazole derivatives (3a–k) were screened for their in vitro activity as platelet aggregation inhibitors.     

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.     

Heterocyclic synthesis with 3-cyano-2(1H)pyridinethione: Synthesis of 3-oxo-2,3-dihydroisothiazolo[5,4-b]pyridine and related compounds

Summary 3-Carbethoxy-4,6-diphenyl-2-pyrridine sulfonamide (5), can be cyclized to 3-oxo-2,3-dihydro-4,6-diphenylisothiazolo[5,4-b]pyridine-1,1-dioxide (2). Oxidation of pyridinethione6 with Cl₂/H₂O gave the sulfonyl chloride derivative7, which can be ammonolyzed to 3-amino-4,6-diphenylisothiazolo[5,4-b]pyridine-1,1-dioxide (8), and 3-cyano-4,6-diphenylpyridine-2-sulfonamide (9). Hydrolysis of6 gave 3-carboxamido-2(1H)pyridinethione (12) which can be oxidized with iodine to 3-oxo-4,6-diphenyl-2,3-dihydroisothiazolo[5,4-b]pyridine (13). 3-Methyl-4,6-diphenylisothiazolo[5,4-b]pyridine-1,1-dioxide (17) was also prepared from6.

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Heterocyclensynthese mit 3-Cyano-2(1H)pyridinthion: Synthese von 3-Oxo-2,3-dihydroisothiazolo-[5,4-b]pyridin und verwandten Verbindungen

Zusammenfassung 3-Carbethoxy-4,6-diphenyl-2-pyridinsulfonamid (5) kann zu 3-Oxo-2,3-dihydro-4,6-diphenylisothiazolo[5,4-b]pyridin-1,1-dioxid (2) cyclisiert werden. Die Oxidation des Pyridinthions6 mit Cl₂/H₂O ergab das Sulfonylchlorid-Derivat7, das mit Ammoniak zu 3-Amino-4,6-diphenylisothiazolo[5,4-b]pyridin-1,1-dioxid (8) und 3-Cyano-4,6-diphenylpyridin-2-sulfonamid (9) umgesetzt werden kann. Die Hydrolyse von6 ergab 3-Carboxamido-2(1H)pyridinthion (12), das mit Jod zu 3-Oxo-4,6-diphenyl-2,3-dihydroisothiazolo[5,4-b]pyridin (13) oxidiert wurde. 3-Methyl-4,6-diphenyl-isothiazolo[5,4-b]pyridin-1,1-dioxid (17) wurde ebenfalls aus6 hergestellt.

     

Neue Derivate der 2-Acylamino-thiophen-(und-benzo[b]thiophen-)-3-carbonsäure sowie des ([1]Benzo-)Thieno[2,3-d]-pyrimidin-4(3H)-ons

The title substances1 and2 were prepared by acylation of the corresponding ethyl 2-amino-thiophene- (or:-4,5,6,7-tetrahydro-benzo[b]thiophene)-3-carboxylates, in some cases followed by reactions introducing a basic substituent.Additionally a group of 2-aroylamino-thiophene-(or:-4,5,6,7-tetrahydro-benzo[b]thiophene)-3-carboxamides was subjected to ring closure reactions, yielding the corresponding 2-aryl-thieno[2,3-d]pyrimidin-4(3H)-ones and 2-aryl-[1]benzothieno[2,3-d]pyrimidin-4(3H)-ones (both:3).

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Zum Teil unter Mitarbeit vonFerdinand Fuhrmann     

Synthesis and Antimicrobial Activities of Some 6-Methyl-3-Thioxo-2,3-Dihydro-1,2,4-Triazine Derivatives

Abstract

4-Arylidene-imidazole derivatives (4a,b) were readily prepared by reacting 4-am- ino-6-methyl-3–thioxo-2,3–dihydro[1,2,4]triazin-5(4H)-one (1) with 4-arylidene-2-phenyl- 4H-oxazol-5-one (2). Reaction of 1 with some aromatic aldehydes in presence of triethylphosphite exclusively afforded the corresponding aminophosphonates 5a-c. Reaction of 1 with 3-phenyl-1H-quinazoline-2,4-dione (6a) and/or 3-phenyl-2-thioxo-2,3-dihydro- 1H-quinazolin-4-one (6b) gave 2-(6-methyl-5-oxo-3-thioxo-2,5-dihydro-3H-[1,2,4]triazin-4-ylimino)-3-phenyl-2,3-dihydro-1H-quinazolin-4-one (7). Moreover, on treating 1 with 2-phenylbenzo[d][1,3]thiazine-4-thione (8), 6-methyl-4-(2-phenyl-4-thioxo-4H-quinazolin-3-yl)-3-thioxo-3,4-dihydro-2H-[1,2,4]triazine-5-one (9) was obtained in 65% yield. Reaction of 1 with 4-sulfonylaminoacetic acid derivatives (10a,b) afforded the corresponding sulfonamides (11a,b), respectively. Acid hydrolysis of 11a afforded 7-aminomethyl-3-methyl[1,3,4]thiadiazole[2,3-c][1,2,4]triazin-4-one (12). 4-Amino-6-methyl-3-(morpholine-4-ylsulfanyl)-4H-[1,2,4]triazin-5-one (14) was prepared by reacting compound 1 with morpholine in presence of KI/I₂, while 3,3′-bis(4-amino-6-methyl-5-oxo-triazinyl)disulfide (16) was obtained by oxidation of 1 with lead tetraacetate. The antimicrobial activity of the products was evaluated against Gram-positive and Gram-negative bacteria as well as the fungus Candida albicans.

[Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental files: Additional text, figures, and tables.]     

Zur Reaktion von 4-Alkylaminodihydro-2(1H)-pyridinthionen bzw. -onen mit Ethylmalonsäure-bis-trichlorphenylester

4-Alkylamino-2(1H)-pyridinethiones (1) react with bis-trichlorphenylethylmalonate (3) to give four isomeric products: 5-thioxo-1,6-naphthyridine-2(1H)-ones (4), 7,7-dimethyl-4H-thiopyrano[2,3-b]pyridine-4-ones (6), 2,2-dimethyl-2H-thiopyrano[2,3-b]pyridine-5,7-dioles (7) and 2,2-dimethyl-2H-thiopyrano[2,3-b]pyridine-5(3H)-ones (8). On treatment with alkali the thioxogroup of4 is hydrolyzed and 1,6-naphthyridinediones (5) are formed. Compound5 can also be synthesized by heating the alkylaminopyridones (2) together with3.6 can be hydrolyzed to 2-thioxo-3-pyridylpropylketones (12). On treatment with diluted alkali or conc. acid the aminogroup of7 and8 is hydrolyzed and10 is formed. By heating in 20% NaOH10 is transformed to the dihydroxymercapto-3-pyridylmethylketone (11).

Herrn Prof. Dr.Erich Ziegler mit den besten Wünschen zum 70. Geburtstag gewidmet.     

Beiträge zur Chemie schwefelhaltiger Heterocyclen, 5. Mitt.: Weitere Reaktionen in der Reihe der 5,6,7,8-Tetrahydro-[1]benzothieno[2,3-d]pyrimidine

Zusammenfassung 2,4-Dioxo-1,2,3,4,5,6,7,8-octahydro-[1]benzothieno[2,3-d]pyrimidin (2) wurde1. durch Umsetzung von 2-Amino-4,5,6,7-tetrahydro-benzo[b]thiophen-3-carbonsäureamid mit Phosgen, 2. durch Ringschlußreaktionen von 2-(N-Carbäthoxy-amino)-4,5,6,7-tetrahydro-benzo[b]thiophen-3-carbonsäureamid sowie 3. durch thermische Cyclisierung von 2-(N-Phenylureido)-4,5,6,7-tetrahydro-benzo[b]thiophen-3-carbonsäureamid gewonnen. Das entsprechende 3-Phenylderivat wurde durch Ringschlußreaktionen des Äthylesters oder des Amides der 2-(N-Phenylureido)-4,5,6,7-tetrahydro-benzo[b]thiophen-3-carbonsäure erhalten.Umsetzung von 2-Amino-4,5,6,7-tetrahydro-benzo[b]thiophen-3-carbonsäureamid mit Chlorkohlensäureester gab je nach den Reaktionsbedingungen entweder 2-(N-Carbäthoxy-amino)-4,5,6,7-tetrahydro-benzo[b]thiophen-3-carbonsäureamid oder 2-Äthoxy-4-oxo-3,4,5,6,7,8-hexahydro-[1]benzothieno[2,3-d]pyrimidin.

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Contributions to the chemistry of sulfur containing heterocycles, V: Further reactions of 5,6,7,8-tetrahydro-[1]benzothieno-[2,3-d]pyrimidines

2,4-Dioxo-1,2,3,4,5,6,7,8-octahydro-[1]benzothieno[2,3-d]pyrimidine was prepared in 3 different ways: by reaction of 2-amino-4,5,6,7-tetrahydro-benzo[b]thiophene-3-carboxamide with phosgene, by cyclization of 2-(N-carbethoxy-amino)-4,5,6,7-tetrahydro-benzo[b]thiophene-3-carboxamide, or by thermal cyclization of ethyl 2-(N-phenylureido)-benzo[b]thiophene-3-carboxylate. The corresponding 3-phenyl derivative was prepared by ring closure reactions of ethyl 2-(N-phenylureido)-4,5,6,7-tetrahydro-benzo[b]thiophene-3-carboxylate or-3-carboxamide. Reaction of 2-amino-4,5,6,7-tetrahydro-benzo[b]thiophene-3-carboxamide with ethyl chloroformate yielded either 2-(N-carbethoxy-amino)-4,5,6,7-tetrahydro-benzo[b]thiophene-3-carboxamide or 2-ethoxy-4-oxo-3,4,5,6,7,8-hexahydro-[1]benzothieno-[2,3-d]pyrimidine depending on reaction conditions.

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Mit 1 Abbildung

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Meinem sehr verehrten Lehrer, Herrn o. Prof. Dr.O. Hromatka, in Dankbarkeit zum 65. Geburtstag gewidmet.

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Aus patentrechtlichen Gründen bis jetzt zurückgehalten.

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4. Mitt.:F. Sauter undA. Dzerovicz, Mh. Chem.100, 913 (1969).     

Ein Beitrag zur Chemie des 2,3-Dihydro-3-oxo-benzo[b]thiophen-1,1-dioxids Synthesen mit Nitrilen, 86. Mitt.

Summary 2,3-Dihydro-3-oxo-benzo[b]thiophen-1,1-dioxide (1) reacts as CH-acidic component with amidines of orthoesters and anilines resp. to give the anilinomethylene derivates3, 4, and5. With triethyl orthoformiate the hydroxymethylene-compound7 is obtained. Anilino- and phenylhydrazino derivates8 and9 prove the carbonyl activity of1, azo-coupling leads to10, whereas treatment of1 with sulfur and malononitrile yields the benzo[b]thieno[2,3-d]thiophenes11. Introduction of substituents with active NH-functions in position 2 of the dicyanomethylene-product2, such as azocoupling, reaction with phenyl isocyanate and formation of enamines, leads to ring closure reactions between a nitrile and the NH-group. Thereby the phenyl-benzo[4,5]thieno[2,3-c]pyridazines12, the phenyl-1H-benzo[4,5]thieno[2,3-c]pyridines13 and the phenylamino-benzo[4,5]thieno[2,3-c]pyridines14 are obtained.¹³C and¹⁵N-NMR spectroscopy was used as proof of the ring closure reactions.

     

A Convenient Synthesis of Novel Functionalized Pyrimido[5′,4′:4,5]thieno[3,2-c]pyridazines and Related Fused Systems

Possible approaches to the synthesis of functionalized, pyrimido[5′,4′:4,5]thieno [3,2-c]pyridazines 2-18 , pyridazino[3′,4′:4,5]thieno[2,3-d]triazines 19, 20a,b and pyrido[3′,2′:4,5]thieno[3,2-c]pyridazines 22a,b are described. The sequence involves the heterocyclization of 6-amino-1,3-diphenyl-1,4-dihydrothieno[3,2-c]pyridazine-7-carboxamide (1) with appropriate reagents. The antimicrobial activity of some the newly synthesized compounds was examined. All tested compounds proved to be active as antibacterial and antifungal agents.     

Fusions of pyrido[4′,3′:4,5]thieno[2,3-d]pyrimidines with N-heterocyclic moieties

Versatile 2-thioxopyrimidine-type building blocks ethyl 3-(2-ethoxy-2-oxoethyl)- 4 -oxo-2-thioxo-1,2,3,4,5,6,7,8-octahydropyrido[4′,3′:4,5]thieno[2,3-d]pyrimidine-7-carboxylate ( 4 ) and ethyl 4-oxo-2-thioxo-1,2,3,4,5,6,7,8-octahydropyrido[4′,3′:4,5]thieno[2,3-d]pyrimidine-7-carboxylate ( 8 ) were synthesized from diethyl 2-amino-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3,6-dicarboxylate ( 1 ). Derivatives of linear and angular heterocyclic systems having the imidazole and 1,2,4-triazole ring were obtained from the key intermediates 4 and 8 , respectively.     

Reactions of 6-Amino-5-Cyano-3-Methyl-1,4-Diphenyl-1H 4H-Pyrano[2,3-C]Pyrazole and its Methanimidate

Reaction of 6-amino-5-cyano-3-methyl-1,4-diphenyl- 1H,4H-pyrano[2,3-c]pyrazole 1 with triethyl orthoformate in acetic anhydride gave its methanimidate 2, which reacts with primary aliphatic and aromatic amines to give 4,6-dihydro-3-methyl-1,4-diphenyl-6- (alkyl)pyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5(lH)- imine 3 and the starting compound 1 , respectively. Treatment of 1 with o-aminophenol gave 5-(2-benzoxalyl)- 1,4-dihydro-3-methyl-1,4-diphenylpyrano[2,3-c]pyrazol- 6-amine 9.     

3-Aminopyrazolo[4,3-c]pyridine-4,6-dione as a precursor for novel pyrazolo[4,5,1-ij][1,6]naphthyridines and pyrido[4’,3’:3,4]pyrazolo[1,5-a]pyrimidines

The versatile, 3-aminopyrazolo[4,3-c]pyridine-4,6-dione (2) was synthesized and allowed to react with aldehydes, aryldiazonium chlorides, chalcones and enaminones to afford regioselectively the novel pyrazolo[4,3-c]pyridine derivatives 4a-c, pyrazolo[4,5,1-ij][1,6] naphthyridines 9a-d and pyrido[4’,3':3,4]pyrazlo[1,5-a]pyrimidines 19a-i. The structure of all the newly synthesized compounds was assigned from elemental analysis and spectral data. Also, the mechanistic aspects for the formation of the newly synthesized compounds is discussed.     

Synthesis and Dehydration of Oxadithia and Trithiadioxime Crown Compounds

The reaction of 2,2‐oxydiethanethiol and 2‐[2‐mercaptoethyl) thio] ethanethiol with dichloroglyoxime (DCGO) in absolute EtOH led to crown compounds, oxadithia (5Z,6Z)‐1,4,7‐oxadithiadiononane‐5,6‐dionedioxime (1) and trithia (2Z,3Z)‐1,4,7‐trithionane‐2,3‐dionedioxime (2), respectively. The compounds 5,6,8,9‐tetrahydro [1,4,7]oxadithionine[5,6‐c][1,2,5]oxadiazole (3) and 5,6,8,9‐tetrahydro[1,4,7]trithionino[2,3‐c][1,2,5]oxadiazole (4) were prepared by dehydration of 1 and 2 in aqueous solution of potassium hydroxide at 170–180°C, respectively.     

[1]Benzofuro[3,2-<Emphasis Type="Italic">c</Emphasis>]pyridine synthesis and coordination reactions

(E)-3-(1-Benzofuran-2-yl)propenoic acid (1) was prepared from 1-benzofuran-2-carbaldehyde under the Doebner’s conditions. The obtained acid was converted to the corresponding azide 2, which was cyclized by heating in diphenyl ether to [1]benzofuro[3,2-c]pyridine-1(2H)-one (3). This compound was aromatized with phosphorus oxychloride to chloroderivative 4 which was reduced with zinc and acetic acid to the title compound 5. [1]Benzofuro[3,2-c]pyridine-2-oxide (6) was synthesized by reaction of 5 with 3-chloroperoxybenzoic acid in dichloromethane. Treatment of 6 with benzoyl chloride and potassium cyanide (Reissert-Henze reaction) was shown to produce the corresponding [1]benzofuro[3,2-c]pyridine-1-carbonitrile (7). The title compound was used for preparation of complexes Cu₂(ac)₄(bfp)₂ (8) and CoCl₂(bfp)₂ (9), where ac=CH₃CO₂⁻ and bfp=[1]benzofuro[3,2-c]pyridine. Both oxygen atom of carboxylate ions is used in the coordination to Cu(II). Thermal properties of the complexes 8 and 9 have been studied by TG and DTA and both complexes exhibited high thermal stability while complex 9 are thermally more stable than complex 8.     

Studies on Quinazolines. Part III. Synthesis of Some Fused-Ring Cationic and Mesoionic Derivatives of the 1,3-Thiazolo[3,2-c]quinazoline Ring System

4-Allylthio-2-arylquinazolines 4a–c undergo cyclization by action of bromine to furnish 5-aryl-3-bromomethyl-2,3-dihydrothiazolo[3,2-c]quinazolin-4-ium bromide 5a–c. Compounds 5a–c undergo ring opening by action of water under acid catalysis to afford the corresponding dibromide derivatives 6a–c. Bromination of 3-allyl-2-aryl-4(3H)quinazolinethiones 7a–c leads to 5-aryl-2-bromomethyl-2,3-dihydrothiazolo[3,2-c]quinazolin-4-ium bromides 8a–c. However, 5-aryl-1,3-thiazolo[3,2-c]quinazolinium-3-olate 10a–c were prepared by the cyclodehydration of the corresponding thioglycolic acids 9a–c with Ac₂O.