Benzazoles and naphthazoles

Coupling p-tolyldiazonium salts with hydrazones of 2-hydrazinonaphth-[1,2-d]thiazole gives the unsymmetrical 1-napth[1, 2-d]thiazolyl-3-aryl(or methyl]-5-p-totylformazans. Conclusions concerning their structure are drawn on the basis of the IR and UV spectral data, and comparisons are made with the isomeric naphth[2, 1-d]thiazole formazans.For Part XXVI, see [4].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1198–1200, September, 1970.     

Benzazoles and naphthazoles

1-Benzothiazolyl-5-(p-nitrophenyl)formazans, which have thermochromic properties, were synthesized. The structure of the compounds was studied by means of IR and UV spectroscopy and quantum-mechanical calculations, the state of the tautomeric equilibrium was established, and the most probable planar conformations of the formazans as a function of the character of the substituent in the 3-position of the formazan chain were found. It is shown that the thermochromism of these compounds in solution is related to dissociation of the hydrogen of the NH bond of the formazan grouping and that the deeply-colored thermally induced form is the anionic aci form.     

Benzazoles and naphthazoles XXXV. Autooxidative coupling of 1-benzyl-2-hydrazinobenzmidazole with nitroformaldehyde arylhydrazones

1-Benzyl-2-hydrazinobenzimidazole undergoes autooxidative coupling with nitroformaldehyde arylhydrazones to give meso-carbon-unsubstituted 1-(1-benzyl-2-benzimidazolyl)-5-arylformazans (instead of the expected formazans with a nitro group in the meso position). Data on the structures and complexing abilities of the new unsymmetrical formazans of the benzimidazole series are presented.See [1] for communication XXXIV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 393–395, March, 1972.     

Benzazoles and naphthazoles XXXIV. Synthesis of mono-, di-, and triheterylformazans by autooxidation of 2-hydrazinobenzazoles

Mono-, di-, and triheteiylformazans were obtained by the autooxidative coupling (in pyridine solution) of 1-alkyl-2-hydrazinobenzimidazoles with the aryl(azolyl)hydrazones of aliphatic or heterocyclic aldehydes.See [1] for communication XXXIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 390–392, March, 1972.     

Research on benz- and naphthazoles

The synthesis of 2-hydrazinonaphth[2, 1-d]thiazole is effected, and its ability to undergo autoxidation in ethanol solution to give 1, 5-di(naphth[2, 1-d]thiazolyl-2)-3-methylformazan is established. Unsymmetrical 1-naphth[2, 1-d]thiazolyl-5-tolyl-3-aryl(or methyl) formazans are obtained by coupling a p-tolyldiazonium compound with the appropriate 2-hydrazinonaphth[2, 1-d]thiazole hydrazones.For Part XIX see [3].     

Investigations of benzazoles and naphthazoles

1-(5-Benzimidazolyl)-5-phenylformazans, which are isomers of the previously obtained 1-(2-benzimidazolyl)-5-phenylformazans, and 1-(5-benzimidazolyl)-5-(2-benzimidazolyl)formazans, which are isomers of 1,5-bis(2-benzimidazolyl)formazans, were synthesized. In contrast to their isomers, the benzimidazole ring in the formazans obtained is connected to the formazan chain at the 5 position rather than at the 2 position, and this leads to substantial differences in the properties, structures, and chromaticities of the isomeric formazans. The imidazole ring in 1-(5-benzimidazolyl)-5-phenylformazans is far removed from the chain and cannot participate in amino-imino tautomerism, in connection with which, the indicated formazans behave like 1,5-diphenylformazans and do not form complexes with metal ions in the cold. For the same reasons, 1-(5-benzimidazolyl)-5-(2-benzimidazolyl)formazans differ from the isomeric symmetrical 1,5-bis(2-benzimidazolyl)formazans by a hipsochromic shift of the long-wave maximum of the spectrum and are similar (with respect to their spectrophotometric characteristics and complexing properties) to the unsymmetrical 1-(2-benzimidazolyl)-5-phenylformazans. Conclusions regarding the state of the hydrogen bond of the formazan chain were drawn on the basis of the IR spectral data.See [1] for communication XXXI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1136–1138, August, 1971.     

Research on benzo- and naphthazoles

Fourteen unsymmetrical 1-(1-alkylbenzoimidazolyl-2)-3-methyl-5-arylformazans are synthesized by nitrogen coupling of aryl diazonium salts with acetaldehyde 1-alkylbenzoimidazolyl-2-hydrazones, and their visible absorption maxima are given.For Part XII see [6].     

Research on benz- and naphthazoles

Heterocyclic analogs of triphenylformazan have been synthesized: 1-(1'-benzylbenzimidazolyl)-3,5-diphenylformazan (I), 1-benzothiazolyl-3,5-diphenylformazan (II), and 1-benzoxazolyl-3,5-diphenylformazan (III). On a basis of the study of IR and UV spectra, the hypothesis has been put forward that I lacks a chelate ring while II and III have chelate rings with a weak intramolecular hydrogen bond. Ease of complex formation with many metals and a capacity for the formation of tetrazolium salts have been noted.For part XXII, see [1].     

Researches on benz-and naphthazoles

Bromosuccinimide converts unsymmetrical 1-(1′-alkylbenzimidazolyl)-5-aryl-3-methylformazans and 1-benzthiazolyl-5-aryl-3-methyl (or aryl)formazans to the corresponding tetrazolium salts. Symmetrical 1,5-di(1′-benzylbenzimidazolyl-2′)-3-methylformazan gives a bromoamine, which is not transformed to a tetrazolium salt, and is separated as a dihydrobromide. For Part XVIII see [9]     

Investigations in the field of benzazoles and naphthazoles

1-(Alkyl benzimidazolyl)-, 1-benzothiazolyl- and 1-benzoxazolyl-3-methyl-5-phenylformazans containing sulfo groups (in the meta or para position) in the phenyl residue have been synthesized. It has been established that some of them can be used as analytical reagents.For part XXI, see [5].     

Interaction Study between ESIPT Fluorescent Lipophile-Based Benzazoles and BSA

In this study, the interactions of ESIPT fluorescent lipophile-based benzazoles with bovine serum albumin (BSA) were studied and their binding affinity was evaluated. In phosphate-buffered saline (PBS) solution these compounds produce absorption maxima in the UV region and a main fluorescence emission with a large Stokes shift in the blue–green regions due to a proton transfer process in the excited state. The interactions of the benzazoles with BSA were studied using UV-Vis absorption and steady-state fluorescence spectroscopy. The observed spectral quenching of BSA indicates that these compounds could bind to BSA through a strong binding affinity afforded by a static quenching mechanism (K_q~10¹² L·mol⁻¹·s⁻¹). The docking simulations indicate that compounds 13 and 16 bind closely to Trp134 in domain I, adopting similar binding poses and interactions. On the other hand, compounds 12, 14, 15, and 17 were bound between domains I and III and did not directly interact with Trp134.     

Benzazoles 5*. Synthesis and arylsulfonylation of 1-hydroxymethylbenzimidazole

1-Hydroxymethylbenzimidazole was synthesized by the reaction of benzimidazole with formaldehyde. Arylsulfonylation of the former in the presence of triethylamine occurred anomalously with deformylation to give 1-arylsulfonylbenzimidazoles in place of the expected 1-arylsulfonyloxymethyl-benzimidazoles.     

Benzazoles: I. Regioselective arylsulfonylation of benzimidazol-2-amine

Benzimidazol-2-amine reacted with arenesulfonyl chlorides in the presence of triethylamine in regioselective fashion at the endocyclic nitrogen atom, the exocyclic amino group remaining intact. The yields of 1-arylsulfonylbenzimidazol-2-amines depend on the electronic properties of substituents in the benzene ring of arenesulfonyl chlorides.     

Researches on benz- and naphthazoles XVII. Unsymmetrical formazans of the benzothiazole and benzoxazole series

1-Benzothiazolyl- and 1-benzoxazolyl-3-methyl(or phenyl)-5-arylformazans are synthesized. The depth of the color of the similarly structured 1-benzazolyl-5-arylformazans depends on the nature of the benzazole group. The power of the chromophores decreases in the following order: 1-alkyl-benzimidazole > benzothiazole > benzoxazole. Unsymmetrical 1-benzazolyl-5-arylformazans exhibit positive solvatochromism.For Part XVI see [3].     

Benzazoles. 3*. Synthesis and arylsulfonylation of 2-substituted benzimidazoles

2-Alkylbenzimidazoles have been obtained from o-nitroaniline and aliphatic carboxylic acids by reductive cyclization. Interaction of the former with arenesulfonyl chlorides led to the synthesis of 2-alkyl-1-arylsulfonylbenzimidazoles, the yield of which depended on the structure of the substituent in position 2.     

Researches on benz- and naphthazoles XVII. Unsymmetrical formazans of the benzothiazole and benzoxazole series

1-Benzothiazolyl- and 1-benzoxazolyl-3-methyl(or phenyl)-5-arylformazans are synthesized. The depth of the color of the similarly structured 1-benzazolyl-5-arylformazans depends on the nature of the benzazole group. The power of the chromophores decreases in the following order: 1-alkyl-benzimidazole > benzothiazole > benzoxazole. Unsymmetrical 1-benzazolyl-5-arylformazans exhibit positive solvatochromism.     

Benzazoles. 4. Synthesis and chemical reactions of 6-chlorosulfonylbenzoxazolin-2-ones

The corresponding 6-chlorosulfonyl derivatives were synthesized from benzoxazolin-2-one and its 3-methyl derivative by treatment with chlorosulfonic acid. By treatment of the compounds obtained with water and other nucleophilic reagents (aliphatic and heterocyclic amines) 2-oxobenzoxazoline-6-sulfonic acids and a series of their amides were obtained, while reduction with SnCl₂·2H₂O gave 6-mercaptobenzoxazolin-2-ones.     

Benzazoles: II. Synthesis and arenesulfonylation of 1-methyl-1H-benzimidazol-2-amine

The reaction of 1-methyl-1H-benzimidazol-2-amine with arenesulfonyl chlorides in the presence of triethylamine afforded 1-arenesulfonyl-3-methyl-2,3-dihydro-1H-benzimidazol-2-imines instead of expected N-(1-methyl-1H-benzimidazol 2-yl)arenesulfonamides.     

Benzazoles. 2. Relative Activity of Catalysts and 4-Substituted Benzoyl Chlorides in the Acylation of Benzothiazolin-2-ones

A series has been established for the relative activity of catalysts and 4-substituted benzoyl chlorides on acylation of benzothiazolin-2-ones with 4-substituted benzoyl chlorides in the presence of FeCl₃, FeCl₃·6H₂O, FeCl₃12H₂O, ZnCl₂, ZnCl₂2H₂O, AlCl₃, and iron acetylacetonate, as a function of the degree of acidity of the catalyst and the electrophilicity of the acylating agent.