2-Aminothiazole derivatives. III. Mass spectra of some 5H-thiazolo [3,2-a] pyrimidin-5-ones

The mass spectra of some 7-methyl, 7-chloro and 6-earbethoxythiazolo[3,2-a]pyrimidin-5-ones were studied ( 2,3,4 ). The electron impact fragmentation patterns of these compounds showed their relatively high stability and their similar mode of decomposition. Certain differences were observed among the three classes of compounds, due to the nature of the substituent on the pyrimidine ring.     

Microwave assisted synthesis of 2,3-dihydro-4H-benzo[4,5]thiazolo[3,2-a]furo[2,3-d]pyrimidin-4-ones and 6,7-dihydro-5H-furo[2,3-d]thiazolo[3,2-a]pyrimidin-5-ones using Mn(OAc)3

2-Hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-one 2a and 7-hydroxy-5H-thiazolo[3,2-a]pyrimidin-5-one 2b, were obtained in high yields under mild conditions from the cyclization reactions of bis-(2,4,6-trichlorophenyl) malonate and 2-aminobenzothiazole or 2-aminothiazole, respectively. A new class of compounds, 2,3-dihydro-4H-benzo[4,5]thiazolo[3,2-a]furo[2,3-d]pyrimidin-4-ones and 6,7-dihydro-5H-furo[2,3-d]thiazolo[3,2-a]pyrimidin-5-ones, were synthesized via the microwave assisted radical addition of compounds 2a and 2b to various alkenes using manganese(III) acetate. A preliminary acetylcholine esterase (AchE) inhibition test of compound 4e showed excellent (92%) inhibitory potential, comparable with the standard drug Donapezil®.     

A novel and convenient synthesis of thiazolo[3,2-a]pyrimidin-7-ones and pyrido[1,2-a]pyrimidin-2-ones using Vilsmeier reagent

A novel route for the synthesis of thiazolo[3,2-a]pyrimidin-7-ones and pyrido[1,2-a]pyrimidin-2-ones from acetylated 2aminothiazoles and 2-aminopyridines under Vilsmeier conditions has been developed.The plausible mechanism has also been proposed.     

Synthesis of 2,3-Dihydrothiazolo[3,2-a]pyrimidin-5-ones by a Michael-type Tandem Reaction

Summary. Although various thiazoles are known in literature for their biological and pharmacological properties only a few multi-step synthesis pathways for the preparation of thiazolo[3,2-a]pyrimidinones have been reported, which are tedious and time-consuming. An alternative synthesis pathway is described, which allows the preparation of 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-ones in a one-step process based on a Michael-type tandem reaction. By heating of 2-thiobarbituric acid with ethyl 4-bromocrotonate in ethanol at 60°C for 2 h, a 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-one was obtained in 73% yield, whereas carrying out the reaction at room temperature results in the formation of an unstable unsaturated ester. The structures of both, the α,β-unsaturated ester as well as the 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-one were confirmed by NMR spectroscopy. Additionally, the structure of the 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-one was investigated by single-crystal X-ray analysis. The described approach offers a significant improvement over previously reported synthesis pathways because it allows the simple preparation of 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-ones with good yields in a one-step reaction.     

Synthesis of 5H-benzothiazolo[3,2-a]quinazolin-5-ones

5H-Benzothiazolo[3,2-a]quinazolin-5-ones (Va-d) were synthesized by thermal cyclization of N-(2-benzothiazolyl)-2-fluorobenzamides (IVa-d) which were obtained by allowing 2-fluorobenzoyl chloride to react with 2-aminobenzothiazoles.     

Syntheses of 5H-benzoxazolo[3,2-a] quinolin-5-ones

Treatment of N-(2-hydroxyphenyl)anthranilic acid with acetic anhydride, under refluxing conditions provided a simple method for the synthesis of 5H-henzoxazolo[3,2-a] quinolin-5-one (IVa), a heretofore unreported ring system. When propionic anhydride was used in the above reaction, 6-methyl-5H-benzoxazolo[3,2-a]quinolin-5-one (Va) was obtained. Other examples prepared in this fashion were IVb, IVc and Vb. Treatment of IVa with methoxyethylamine afforded 1,2-dihydro-1-(2-hydroxyphenyl)-2-(methoxyethylimino)-4-quinolinol (VII). A possible mechanism for the cyclization reaction is discussed.     

Synthesis of 5H-benzoxazolo[3,2-a]quinazolin-5-ones

5H-Benzoxazolo[3,2-a]quinazolin-5-ones (Xa-d) were synthesized in excellent yields from N-(2-hydroxyphenyl)anthranilic acids (Ia-d) and cyanogen bromide. The synthesis was based on the mechanistic consideration of the reactions of salicylic acid with cyanogen bromide previously reported in the literature. A versatile alternative route to these novel heterocyclic compounds was through thermal cyclization of N-(2-benzoxazolyl)-2-fluorobenzamides (XIII) obtained by reacting 2-fluorobenzoyl chloride with 2-aminobenzoxazoles. The reaction of Xb with ethanol in the presence of potassium hydroxide gave an ethoxyquinazolinone (XVII). Similarly, the alkaline hydrolysis of Xb afforded an quinazolindione (XVIII).     

Synthesis of 5H-[1,3]thiazolo[3,2-a]pyrimidin-5-one derivatives

The reaction of 2-aminothiazoles with ethyl acetoacetate in acetic or polyphosphoric acid gave a series of 5H-[1,3]thiazolo[3,2-a]pyrimidin-5-one derivatives which were nitrated with a mixture of nitric and sulfuric acid to 6-nitro-5H-[1,3]thiazolo[3,2-a]pyrimidin-5-ones, and the latter were reduced to the corresponding amines.     

Mass spectrometry of N-substituted amino acids and their derivatives: Correlation of the abundances of the M+. and selected fragment ions of metamers

The mass spectral fragmentations of nineteen new metameric N-(E)-stilbenyloxyalkylcarbonyl- [or (E)-(4′-chlorostilbenyloxyalkylcarbonyl)]-substituted amino acids and their metameric methyl esters and hydrazides were investigated. Fragmentation pathways are proposed on the basis of accurate mass and metastable transition measurements. The correlation between the intensities of M^+. and the selected fragment ions of these compounds is discussed. The data obtained create the basis for distinguishing metamers.     

A Three-Component Synthesis of trifluoromethylated hexahydropyrrolo[1,2-a]imidazol-5-ones and hexahydropyrrolo[1,2-a]pyrimidin-6-ones

Chemistry of Heterocyclic Compounds - A three-component reaction of ethyl trifluoropyruvate, methyl ketones, and ethylenediamine or 1,3-diaminopropane afforded...     

Tetrahydro- and octahydropyrido[1,2-a]pyrimidin-4-ones

The catalytic hydrogenation of 2-methyl-, 1 2,8-dimethyl-, 2 , 2,9-dimethyl-, 3 , 9-methyl-2-propyl-, 4 , 2,3,9-trimethyl-, 5 , 9-methyl-2-phenyl-, 6 , 9-hydroxy-2-methyl-, 7 , 9-acetoxy-2-methyl, 8 , 9-carboxy-2-methyl-, 16 , 9-carboethoxy-2-methyl-, 17 , 9-carbomethoxy-2-methyl-, 18 , and several 9-carboxamido-2-methyl-, 19, 20 , and 21 , derivatives of the pyrido[1,2-a]pyrimidin-4-one heterocycle has led to a series of novel 6,7,8,9-tetrahydro- and fully saturated, octahydro analogs. In deuteriochloroform or DMSO-d₆ solution, the pmr spectra of the tetrahydro derivatives derived from 1-7 revealed only the 6,7,8,9-tetrahydro structures. In the pmr spectra of 16-21 , there was evidence of a facile 1,3-prototropic shift of the proton from position-9 to position-1, resulting in equilibria between tautomeric species, i.e., . The ratio of tautomers present at equilibrium, with the esters, favored the enamine conformation, whereas, with both the carboxylic acid and the amides, the imine structure predominated. Supportive evidence for the enamine structure with the esters was derived also from the ir spectra. Alkylation of the anion derived from the tetrahydro 9-carbomethoxy derivative with sodium hydride led exclusively to derivatives of 6,7,8,9-tetrahydro system.     

Synthesis of[1,2,4]Oxadiazolo[4,5-a]thiazolo[2,3-b]pyrimidin-9(10H)-ones via 1,3-Dipolar Cycloaddition of Nitrile Oxide to Thiazolo[3,2-a]pyrimidin-3-one Derivatives

A new class of [1,2,4]oxadiazolo[4,5‐a]thiazolo[2,3‐b]pyrimidin‐9(10H)‐one was prepared in moderate yields by the reaction of nitrile oxide with 2‐arylmethylidene‐6,7‐dihydro‐5H‐thiazolo[3,2‐a]pyrimidin‐3‐one. The reaction site of dipolarphile is the C?N of thiazolo[3,2‐a]pyrimidin‐3‐one rather than the expected C?C of arylmethylidene. The structures of the products were characterized thoroughly by IR, elemental analysis, MS, and NMR analysis.     

Synthesis and transformations of hydrazinecarbo-dithioates containing the 7-methyl-,5-oxo-5h-1,3,4 thiadiazolo[3,2-a]pyrimidin-2-yl fragment

The reaction of 2-hydrazino-7-methyl-5-ozo-5H-1,3,4-thiadiazolo[3,2-a]pyrimidine with carbon disulfide leads to the formation of hydrazinecarbodithioates and their cyclization products.V. I. Nikitina Institute of Chemistry, Academy of Sciences of the Republic of Tadzikistan, Dushanbe 734063. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 560–562, April, 1994. Original article submitted December 13, 1993.     

Convenient Synthesis of Fluorine-Containing 2-Aryl-5H-[1,3,4]thiadiazolo[3,2-a]quinazolin-5-ones

Russian Journal of Organic Chemistry - An efficient synthetic approach to new fluorine-containing [1,3,4]thiadiazolo[3,2-a]quinazolin-5-ones has been developed on the basis of intramolecular...     

Electron impact mass spectrometry of some 6-substituted tetrazolo[1,5-c]pyrimidin-5(6H)-ones

The electron impact mass spectra of 6-methyltetrazolo[1,5-c]pyrimidin-5(6H)-one, its 7- and 8-methyl derivatives, three 8-halo derivatives and two related nucleosides are reported. On the basis of the high-resolution data and detected metastable ions, the fragmentation routes of their molecular ions are proposed. Coexistence of the tautomeric forms of the title compounds of cyclic (tetrazole) or linear (azide) structure can be suggested owing to the fragmentation pathways identified for the bases. Decomposition of the related nucleosides lies in the breaking of nucleoside bonds to produce the appropriate base and sugar fragments.     

Microwave-Assisted Synthesis and Antifungal Activities of Polysubstituted Furo[3,2-c]chromen-4-ones and 7,8,9,10-Tetrahydro-6H-benzofuro[3,2-c]chromen-6-ones

An efficient and novel microwave-assisted synthesis of furo[3,2-c]chromen-4-ones and 7,8,9,10-tetrahydro-6H-benzofuro[3,2-c]chromen-6-ones via 4-hydroxycoumarins with α-chloroketones or α-bromocyclohexanone in the presence of acetic acid (AcOH)/ammonium acetate (NH₄OAc) using DMF as solvent under microwave irradiation is described. Systematically, antifungal biological tests showed that most of the compounds exhibited potent antifungal activity against Botrytis cinerea, Collecterichum capsica, Alternaria solani, Gibberella zeae, and Rhizoctorzia solani at the concentration of 50 µg/mL. The corresponding EC50 values of these analogues have been detected, and compound 4i showed better antifungal activity against tested fungi Botrytis cinerea and Collecterichum capsica than the reference Osthol.     

Synthesis of 5H-thiazolo[3,2-a]pyrimidine derivatives from 6-methyl-2-thiouracil and 1-acyl-2-bromoacetylenes. X-ray structural study of 3-benzoyl-7-methyl-5H-thiazolo[3,2-a]pyrimidin-5-one

3-Acyl-7-methyl-5H-thiazolo[3,2-a]pyrimidin-5-ones were synthesized by the reaction of 1-acyl-2-bromoacetylenes with 6-methyl-2-thiouracil, carried out with heating in DMF, dioxane, or acetonitrile in the presence of triethylamine. The structure of 3-benzoyl-7-methyl-5H-thiazolo[3,2-a]pyrimidin-5-one was established by X-ray structural analysis.Deceased in 1995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2306–2308, September, 1996.     

Regioselective Synthesis of 3-Benzylthiazolo[3,2-a]pyrimidones and 3-Benzyl-thiazolo[3,2-c]pyrimidones Through Palladium-Catalyzed Heteroannulation of Acetylenic Compounds

Abstract

The reaction of 2-(prop-2-ynylsulfanyl)pyrimidone 1 with various iodobenzenes in the presence of a palladium catalyst leads to regioselective cyclization to 3-benzylthiazolo [3,2-a] pyrimidones 3. The reaction of 4-(prop-2-ynylsulfanyl) pyrimidone 5 with various iodobenzenes in the same condition give the corresponding 3-benzylthiazolo[3,2-c]pyrimidones 6.