Synthesis of 4H-1,3-benzoxazin-4-ones from 2,2-diazidobenzofuran-3(2H)-ones

Benzoxazine derivatives are useful building blocks and display various biological activities. We serendipitously discovered and subsequently developed a new one pot method for the synthesis of 2-(dimethyl amino)/2-morpholino/2- (piperidin-1-yl)-4H-benzo[e][1,3]oxazin-4-ones from corresponding substituted 2,2-diazidobenzofuran 3(2H) - ones and N-formyl dimethyl amine (DMF)/N-formylmorpholine/N-formylpiperidine using m-CPBA at 100?°C in moderate to good yields. We also demonstrated the utility of 4H-benzoxazines for the synthesis of other medicinally important compounds such as 2-hydroxyphenyl substituted 1,2,4-triazoles, unsymmetrical 1,3,5-triazines, and 1,2,4-oxadiazoles.     

Photochemical synthesis of triazolo[3,4-b]-1,3(4H)-benzothiazines: a detailed mechanistic study on photocyclization/photodesulfurisation of triazole-3-thiones

Irradiation of 4-(2-halobenzyl)-5-substituted-1,2,4-triazole-3-thiones under base mediated (CH₃CN/2 M NaOH) condition afforded triazolo[3,4-b]-1,3(4H)-benzothiazines and desulfurized triazoles. Benzophenone sensitized photolysis of triazole-3-thiones gave desulfurized triazoles exclusively. The mechanism of the photocyclization/photodesulfurization and the involvement of singlet and triplet energy levels are discussed.     

Reaction of 3-oxo-N-phenylbutanethioamide with 5-amino-1H-1,2,4-triazoles

Reactions of 3-oxo-N-phenylbutanethioamide with 3-substituted 5-amino-1H-1,2,4-triazoles in acetic acid led to the formation of 5-methyl-7,8-dihydro[1,2,4]triazolo[1,5-a]pyrimidine-7-thiones, 7-methyl-5,8-dihydrol[1,2,4]triazolo[1,5-a]pyrimidine-5-thiones and 7-methyl-5-phenylamino[1,2,4]triazolo[1,5-a]pyrimidines. The structure of the products was proved by the ¹H and ¹³C NMR spectra, X-ray diffraction data, and chemical transformations.     

Solid-phase synthesis of 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-thiones and 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-ones

An efficient approach for the synthesis of 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-thiones and 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-ones on solid phase has been developed. The reaction conditions were readily amenable and the products were obtained in good yields and purities after their cleavage from the resin.     

Efficiency of alkoxyl radical product formation from 5-substituted 3-alkoxy-4-methylthiazole-2(3H)-thiones

In a comparative study, reactions between 5-(p-methoxyphenyl)-substituted 3-alkoxy-4-methylthiazole-2(3H)-thiones and appropriate mediators (BrCCl₃, Bu₃SnH) provided higher yields of alkoxyl radical products (δ-bromohydrins, cyclic ethers, carbonyl compounds) than respective transformations of 5-phenyl- and 5-methyl-substituted derivatives. The unusual selectivity of applied thiohydroxamates to furnish products of O-alkylation, even upon treatment with soft carbon electrophiles, and the marked propensity of 3-alkoxy-5-(p-methoxyphenyl)-4-methylthiazole-2(3H)-thiones to crystallize, facilitated preparation and purification of the new family of alkoxyl radical precursors in a noteworthy manner.     

Synthesis of heterocycles. Part VI. Synthesis and antimicrobial activity of some 4-amino-5-aryl-1,2,4-triazole-3-thiones and their derivatives

4-Amino-5-aryi-1,2,4-triazole-3-thiones I react with acid chlorides to yield 4-acylamino-5-aryl-1,2,4-triazole-3-thiones II. Compounds I also react with methylene iodide, chloroacetonitrile and methyl bromoacetate to give bis-(4-amino-5-aryl-1,2,4-triazol-3-ylthio)methanes III, 4-amino-5-aryl-3-cyanomethylthio-1,2,4-triazoles IV and 4-amino-5-aryl-3-carbomethoxymethylthio-1,2,4-triazoles V, respectively. Compounds V react with hydrazine hydrate to give the corresponding acid hydrazides VI which in turn condenses with acid chlorides and aldehydes to afford respectively 1-[(4-amino-5-aryl-1,2,4-triazol-3-ylthio)acetyl]-2-aroylhydrazines VII and aryl methylene (4-amino-5-aryl-1,2,4-triazol-3-ylthio)acethydrazones VIII. The antimicrobial activities of the above compounds were screened against different strains of bacteria and fungi.     

A one-pot synthesis and 1,3-dipolar cycloaddition of [1,2]dithiolo[4,3-b]indole-3(4H)-thiones

Treatment of N-substituted 2-methyl-1H-indoles 1 with S₂Cl₂ and DABCO in chloroform gave the corresponding [1,2]dithiolo[4,3-b]indole-3(4H)-thiones 5 by the addition of triethylamine in high yield. 1,2-Dithiole-3-thiones 5 underwent cycloaddition with one or two DMAD equivalents to afford either 2-(3-thioxo-1,3-dihydro-2H-indol-2-ylidene)-1,3-dithioles 10 or fused 4,5-dihydrothiopyrano[3,2-b]indoles 9.     

Regioselective alkylation of 1H-7-ethoxycarbonyl-6-methyl-3-phenyl-pyrazolo[5,1-c][1,2,4]triazole and 1H-6-methyl-3-phenyl-pyrazolo[5,1-c][1,2,4]triazole

Alkylation of 1H-6-methyl-3-phenyl-pyrazolo[5,1-c][1,2,4]triazole and 1H-7-ethoxycarbonyl-6-methyl-3-phenyl-pyrazolo[5,1-c][1,2,4]triazole using different alkylating agents leads regioselectively to 1-N-alkylated products. The hydrolysis-decarboxylation of 1,6-dimethyl-7-ethoxycarbonyl-pyrazolo[5,1-c][1,2,4]triazole yields a compound identical with that obtained by the direct methylation of 1H-6-methyl-3-phenyl-pyrazolo[5,1-c][1,2,4]triazole. The 1-N-alkylation is confirmed by NMR spectroscopy and mass spectrometry.     

Stereoselective reductions of N-Boc-hexahydro-1H-indolin-5(6H)-ones

We report the divergent effects of a 3a-methyl and 3a-phenyl substituent on the chemoselectivity and stereoselectivity of reduction of the enamide moiety of N-Boc-hexahydro-1H-indolin-5(6H)-ones. Under ionic reduction conditions (triethylsilane/trifluoroacetic acid) the enamide group of 3a-methyl-N-Boc-hexahydro-1H-indolin-5(6H)-one was reduced to afford exclusively a cis ring-fused product. For the 3a-phenyl substituted analogue more forcing conditions (sodium cyanoborohydride at pH 2-2.5) were required and resulted in the selective reduction of the enamide group to give a trans ring-fused product as well as reduction of the ketone group.     

Non-catalyzed addition of heterocyclic thiols and 5-substituted-1H-tetrazoles to vinyl ethers

The alkylation of 1-substituted 1H-tetrazole-5-thiols and 4-substituted 4 H-1,2,4-triazole-3-thiols with alkyl halides or sulfonates lead to the formation of S-alkylated products regardless of the substituent on the heterocycle. In this work, we found that substituted 1H-tetrazole-5-thiols and 4 H-1,2,4-triazole-3-thiols readily reacted with vinyl ethers in the absence of a catalyst to exclusively form N-substituted 1H-tetrazole-5(4H)-thiones and 1H-1,2,4-triazole-5(4H)-thiones, respectively. Furthermore, the reactions of 5-substituted-1H-tetrazoles with vinyl ethers under the same conditions selectively yielded 2,5-disubstitued tetrazoles.     

Spin trapping of alkoxyl radicals generated from 5-methyl and 5-aryl-3-alkoxy-4-methylthiazole-2(3H)-thiones in photochemically induced and microwave-initiated reactions

Methoxyl and isopropoxyl radicals were generated from N-alkoxy-4,5-dimethylthiazole-2(3H)-thiones (λ_max∼320 nm) and 5-aryl derivatives (aryl=p-XC₆H₄; X=MeO, H, AcNH, Cl) (λ_max∼335 nm) in photochemically and microwave-induced reactions. Alkoxyl radicals were trapped with dimethylpyrrolidine N-oxide and characterized as spin adducts via EPR. Cumyloxyl radicals were liberated in a similar manner from N-cumyloxy-5-(4-methoxyphenyl)-4-methylthiazole-2(3H)-thione. A noteworthy bathochromic shift was found for the lowest energy transition of N-(hydroxy)indeno[2,1-d]thiazole-2(3H)-thione (λ_max=376 nm), if compared to the UV-vis absorption of N-hydroxy-4-methyl-5-phenylthiazole-2(3H)-thione (λ_max=338 nm). Syntheses of alkoxyl radical precursors and procedures for conducting N,O-homolysis are described in a full account.     

4-Amino-3-pentadecyl-3H-1,2,4-triazole-3-thiones and 3-pentadecyl-1,3,4-oxadiazole-2(3H)-thione for the preparation of dimeric palladium(II) complexes and their applications in Tsuji–Trost and Mizoroki–Heck reactions

The synthesis of palladium complexes derived from 4-amino-3-pentadecyl-3H-1,2,4-triazole-3-thiones and 3-pentadecyl-1,3,4-oxadiazole-2(3H)-thiones are reported. They were obtained from palladium acetate and dipotassium tetrachloropalladate(II) and their composition was assigned by elemental analysis (solid state). The resulting metallic entities were also characterized in solution based in mass spectrometry experiments. Their application in organic synthesis as cross-coupling reaction catalysts is described. One example of both conventional Tsuji–Trost and Mizoroki–Heck reactions were efficiently carried out in very high chemical yield.     

Synthesis of 4-(pyrazol-5-yl)-1,2,4-triazole-3-thiones

Condensation of pyrazolyl isothiocyanates 2 with N-substituted hydrazines provided the 2-methyl/phenyl-4-(pyrazol-5-yl)thiosemicarbazides 3 . Cyclization of 3 with formic acid-acetic anhydride or with triethyl orthoacetate-acetic anhydride provided 4-(pyrazol-5-yl)-l,2,4-triazole-3-thiones 4a-f and 5-methyl-4-(pyrazol-5-yl)-1,2,4-triazole-3-thiones 4g-I respectively.     

Reaction of 1-alkyl/aryl-3-amino-1H,3H-quinoline-2,4-diones with urea. Synthetic route to novel 3-(3-acylureido)-2,3-dihydro-1H-indol-2-ones, 4-alkylidene-1′H-spiro[imidazolidine-5,3′-indole]-2,2′-diones, and 3,3a-dihydro-5H-imidazo[4,5-c]quinoline-2,4-diones

1-Substituted 3-alkyl/aryl-3-amino-1H,3H-quinoline-2,4-diones react with urea in boiling acetic acid to give products depending on the type of substitution in position 3 and at the nitrogen atom of the 3-amino group. Starting compounds bearing a primary amino group in position 3 give 3-(3-acylureido)-2,3-dihydro-1H-indol-2-ones. Starting compounds bearing a secondary amino group in position 3 react according to the character of the other substituent in position 3. If there is a hydrogen atom α to the carbon atom C(3), 4-alkylidene-1′H-spiro[imidazolidine-5,3′-indole]-2,2′-diones arise. If a hydrogen atom is not present in this position, the reaction leads to 3,3a-dihydro-5H-imidazo[4,5-c]quinoline-2,4-diones. Reaction mechanisms for these transformations are proposed. All compounds were characterized by their ¹H, ¹³C, IR and atmospheric pressure chemical ionization mass spectra and some of them also by ¹⁵N NMR data.     

Reaction of polychloroacetaldehyde arylsulfonylimines with 2-amino-6<Emphasis Type="Italic">H</Emphasis>-1,3-thiazine-6-thiones and 2-amino-4-phenyl-6<Emphasis Type="Italic">H</Emphasis>-1,3-thiazin-6-one

2-Amino-4-R-6H-1,3-thiazine-6-thiones and 2-amino-4-phenyl-6H-1,3-thiazin-6-one react with highly electrophilic N-arylsulfonylimines of chloral and phenyldichloroacetic aldehyde at the exocyclic amino group affording in good yields products of nucleophilic addition to the azomethine group of imines: N-[2-polychloro-1-(6-thioxo-4-R-6H-1,3-thiazin-2-ylamino)ethyl]- or -[2-polychloro-1-(6-oxo-4-phenyl-6H-1,3-thiazin-2-ylamino)ethyl]arenesulfonamides.     

Highly regioselective heterocyclization reactions of 1H-1,2,4-triazole-3-thiols with chloroacetylenephosphonates

1-Chloroacetylene-2-phosphonates react with 1H-1,2,4-triazole-3-thiols in anhydrous acetonitrile with high regioselectivity to form the fused heterocycles, 6-(dialkoxyphosphoryl)-3H-thiazolo[3,2-b][1,2,4]triazol-7-ylium chlorides 1-5. A significant difference from the previously known reactions of binucleophiles with haloacetylenes is the involvement of both acetylenic carbon atoms in the heterocycle formation. A reaction mechanism is hypothesized that assumes the formation of a sulfenium cation at the acetylene C-1 atom followed by attack of the C-2 atom by the ring N-2 atom. Compounds 1-5 easily lose one alkyl group from the dialkoxyphosphoryl fragment to form zwitterions (e.g., 6-8) which further can be transformed into inner salts 9 and 10 when heated with concentrated hydrochloric acid.     

Synthesis and anticancer activity studies of novel 1-(2,3-dihydro-5H-1,4-benzodioxepin-3-yl)uracil and (6′-substituted)-7- or 9-(2,3-dihydro-5H-1,4-benzodioxepin-3-yl)-7H- or 9H-purines

On the basis of a molecular variation on an isosteric replacement (F→H) from the prototype (RS)-1-(2,3-dihydro-5H-1,4-benzodioxepin-3-yl)-5-fluorouracil, the derivative (RS)-1-(2,3-dihydro-5H-1,4-benzodioxepin-3-yl)uracil 4 was prepared. Later on, the pyrimidine base was substituted by the purine moiety with the objective of increasing both the lipophilicity and the structural diversity of the target molecules. The 6′-halogen substituent of the (RS)-9- or 7-(2,3-dihydro-5H-1,4-benzodioxepin-3-yl)-9H- or 7H-purines shows an interesting reactivity, which is presented and discussed. The anticarcinogenic potential of the target molecules is reported against the MCF-7 cancer cell line.     

Synthesis of 3-amino-5H-pyrrolo[2,3-e]-1,2,4-triazines by Sonogashira/copper(I)-catalyzed heteroannulation

A Sonogashira/copper(I)-catalyzed heteroannulation sequence was developed to convert 3,5-diamino-6-chloro-1,2,4-triazines to the corresponding 3-amino-5H-pyrrolo[2,3-e]-1,2,4-triazine derivatives in good yields.     

Unusual conversion of substituted-3-formylchromones to 3-(5-phenyl-3H-[1,2,4]dithiazol-3-yl)chromen-4-ones: a facile and efficient route to novel 1,2,4-dithiazoles

Substituted 3-formylchromones react with 2-phenyl-4-dimethylamino-1-thia-3-azabuta-1,3-diene (4) or thio-benzamide (7) by heating their toluene solution in a sealed tube to give novel substituted 3-(5-phenyl-3H-[1,2,4]dithiazol-3-yl)chromen-4-ones (6a-e) in high yields.     

One-pot,microwave-assisted synthesis of polymethylene-bridged bis(1H-1,2,4-triazol-5(3)-amines) and their tautomerism

A highly selective and efficient method for the synthesis of 3,3′(5,5′)-polymethylene-bis(1H-1,2,4-triazol-5(3)-amines) was developed using the reaction of dicarboxylic acids and aminoguanidine in an aqueous medium. This one-pot, microwave-promoted method was proved to be scalable affording the desired products in good yields and purity. The scope of the method was successfully explored by the preparation of a small library of polymethylene-bis(1H-1,2,4-triazol-5(3)-amines) with different alkyl chain linkers. The annular prototropic tautomerism in the prepared compounds was studied using NMR spectroscopy and X-ray crystallography.