An analysis on the transmission of electron density through sulphur atoms in the quaternization reactions of benzothiazoles

The kinetics of quaternization of a number of 2-substituted benzothiazoles with alkyl iodides and phenacyl bromide have been studied in nitrobenzene. The order of reactivity of different substituted benzothiazoles has been found to be -H > NO₂ > Cl. The relative reactivity of 2-amino and 2-methyl derivatives has been ascribed to a solvation phenomenon. The analysis of rho values from the Hammett equation suggests two possible routes for the transmission of electron density.     

Heterocyclic Quinones in the Nenitzescu Reaction. Synthesis of Furo- and Pyrrolobenzothiazoles from 2-Methyl-4,7-dioxobenzothiazole

Treatment of the enamines of acetylacetone and benzoylacetone with 2-methyl-4,7-dioxobenzothiazole under Nenitzescu reaction conditions gave furo[2,3-e]benzothiazoles (in acetic acid) and pyrrolo[2,3-e]benzothiazoles (in nitromethane). Using enamines of acetoacetic ester gave exclusively pyrrolo[2,3-e]benzothiazoles.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 252–258, February, 2005.     

Solid-phase synthesis of benzothiazoles using an alkoxyamine linker

An alkoxyamine linker was applied for the solid-phase synthesis of benzothiazoles. The substrate was anchored by aldoxime linkage and products were cleaved from the solid-support by aldoxime-imine exchange coupled with air-oxidation under the weakly acidic conditions. The tether is highly robust under Mitsunobu reaction, nucleophilic substitution reaction, and Pd-catalyzed reaction conditions.     

Synthesis of 2-substituted benzothiazoles via the Brønsted acid catalyzed cyclization of 2-amino thiophenols with nitriles

A convenient and efficient method for the synthesis of 2-substituted benzothiazoles from simple and readily available 2-amino thiophenols and nitriles is described. The Brønsted acid-catalyzed cyclization reaction was performed under metal and solvent-free conditions.     

An efficient protocol for the synthesis of benzoheterocyclic compounds via solid-state melt reaction (SSMR)

An efficient protocol for the synthesis of biologically active benzoheterocyclic compounds such as benzothiazoles, benzimidazoles, benzospirothiazoles, and quinoxaline scaffolds have been accomplished via solid state melt reaction (SSMR) with excellent yields. The new protocol does not require any catalyst, solvent, and workup. Two anti-tumor agents have been prepared to demonstrate the application of this new method.     

Diversity oriented synthesis of benzoxazoles and benzothiazoles

A combinatorial synthetic route yielding benzoxazoles and benzothiazoles is described. The use of o-halophenylisocyanides in the Ugi reaction (U-4CR) followed by a copper-catalyzed cyclization affords the benzoxazole as well as the benzothiazole moiety in good yield and high diversity.     

Metal-free photo-induced radical C-P and C-S bond formation for the synthesis of 2-phosphoryl benzothiazoles

We reveal here a visible-light promoted phosphorylation of 2-isocyanoaryl thioethers for the first time with concomitant C(sp³)-S bond cleavage and imidoyl C–S formation. Additionally, this method features the use of 3 mol% organic dye Rose Bengal as the photocatalyst without external transition-metal or peroxide oxidants, and provides a novel and environmentally friendly approach for the preparation of a variety of 2-phosphoryl benzothiazoles in moderate to good yields.     

Copper promoted C-S and C-N cross-coupling Reactions:The synthesis of 2-(N-Aryolamino)benzothiazoles and 2-(N-Aryolamino)benzimidazoles

The synthesis of 2-(N-aryolamino)benzothiazoles and 2-(N-aryolamino)benzimidazoles has been accomplished in the presence of copper catalyst. These reactions involve C-S and C-N cross-coupling reaction. All electron donating and withdrawing substituent's readily underwent the reaction to give target products in good to excellent yield. In addition, the reaction also gave target product in high yield with bulk scale.     

Synthesis of new amidino-substituted 2-aminothiophenoles: mild basic ring opening of benzothiazole

The efficient synthesis of new amidino, N-isopropylamidino, 2-imidazolinyl substituted benzothiazoles and 2-aminothiophenoles by the Pinner reaction is described. The novel ring opening of benzothiazole with ammonia and ethylenediamine was found, and a plausible reaction mechanism proposed. The ring opening with ethylenediamine is selective and applicable to compounds bearing hydrolytically and amonolytically unstable substituents. Different amidino-substituted 2-aminothiophenoles were isolated in zwitterionic and disulfide form and their structures were determined by X-ray crystal structure analysis.     

A convenient synthesis of 2-acyl benzothiazoles/thiazoles from benzothiazole/thiazole and N,N'-carbonyldiimidazole activated carboxylic acids

A convenient and efficient strategy for the synthesis of 2-acyl benzothiazoles/thiazoles has been developed. The treatment of benzothiazole/thiazole with allylic Grignard reagents readily generates the corresponding 2-Grignard reagents, which is followed by a reaction with N,N'-carbonyldiimidazole activated carboxylic acids to afford various 2-acyl benzothiazoles/thiazoles products. The synthetic method is applicable to a wide array of carboxylic acids and allows easy access to 2-acyl benzothiazoles/thiazoles with considerable yields under mild reaction conditions.     

Synthesis of benzothiazoles via ipso substitution of ortho-methoxythiobenzamides

An efficient route to the synthesis of benzothiazoles from ortho-methoxythiobenzamides via the ipso substitution of an aromatic methoxy group is presented, and the mechanism of the Jacobson synthesis of benzothiazoles is further investigated.     

Metal free montmorillonite KSF clay catalyzed practical synthesis of benzoxazoles and benzothiazoles under aerobic conditions

An efficient method for the synthesis of benzoxazoles and benzothiazoles via montmorillonite KSF clay catalyzed condensation reaction between 2-aminophenols or 2-aminothiophenols and β-diketones is reported. The efficiency of the reaction reflects from the wide substrate scope with electronic differentiation on aryls. The reaction is metal free and proceeds without the exclusion of air or moisture, and further the catalyst can be recycled up to 3–5 catalytic cycles.     

Copper-catalyzed solvent-free redox condensation of benzothiazoles with aldehydes or benzylic alcohols

An efficient and practical method for the construction of 2-aryl- and 2-alkyl-substituted benzothiazoles via a copper-catalyzed redox condensation process between benzothiazoles and aldehydes or benzylic alcohols has been developed. The reaction proceeded under mild reaction conditions using environmentally benign tert-butyl hydroperoxide (TBHP) as the oxidant. A reaction mechanism involving the ring-opening of benzothiazoles initiated by the attack of acyl radical on the thiazole ring and intramolecular condensation is proposed based on the isolation of an anilide disulfide intermediate.     

One-pot synthesis of dihydropyrimidines via eco-friendly phosphorus derivatives catalysis

A straightforward, cost effective and eco-friendly protocol for the Biginelli reaction relying on the use of readily available hypophosphorous acid is presented. The methodology developed displays improvements compared to existing methods, is high-yielding, robust and was applied to a panel of dihydropyrimidines and thio-derivatives with various substituents. Related urea derivatives such as guanidines, benzimidazoles and benzothiazoles also reacted efficiently to afford more complex scaffolds. Thus, this rapid and convenient catalysis allows access to a wide diversity of structures including original biologically relevant heterocycles.     

Synthesis of 2- and 2,5-substituted benzoxazoles and benzothiazoles

A number of 2- and 2,5-perfluoroalkyl and perfluoroalkylether substituted benzoxazoles and benzothiazoles have been prepared. Their relative hydrolytic stability has been examined. In all cases the benzothiazoles were more stable that the benzoxazoles. Substituents in the 2-position offering steric hindrance improve hydrolytic stability.     

A simple approach to benzothiazoles from 2-chloronitrobenzene,elemental sulfur,and aliphatic amine under solvent-free and catalyst-free conditions

A novel solvent-free and catalyst-free synthesis of benzothiazoles from 2-chloronitrobenzene, elemental sulfur, and aliphatic amine has been developed. The reaction tolerated a wide range of functionalities, and various benzothiazoles were synthesized in moderate to good yields in the absence of external oxidant or reductant.     

Synthesis of 2-Aryl Benzothiazoles via K(2)S(2)O(8)-mediated Oxidative Condensation of Benzothiazoles with Aryl Aldehydes

Nontransition metal-catalyzed synthesis of 2-aryl benzothiazoles was achieved through K(2)S(2)O(8)-mediated oxidative condensation of benzothiazoles with aryl aldehydes. The same transformation can also be effected when the aryl aldehydes were replaced with phenylglyoxylic acids.     

水相铜催化α-酮酸与邻氨基苯硫酚合成苯并噻唑化合物

发展了一种新颖的水相α-酮酸与邻氨基苯硫酚合成苯并噻唑化合物的方法。在CuCl₂•2H₂O的催化下,通过该反应顺利合成了2-取代苯并噻唑化合物,产率较高,底物适应性较好。      

A novel practical synthesis of benzothiazoles via Pd-catalyzed thiol cross-coupling

A convenient synthesis of substituted benzothiazoles from 2-bromoanilides has been accomplished. The various 2-bromoanilides were reacted with an alkyl thiolate in high yields using a palladium catalyst. The resulting sulfides were easily converted to the corresponding benzothiazoles via the simultaneous generation of thiols and condensation under basic or acidic conditions.     

Oxidative ring-expansion of benzothiazolines into 1,4-benzothiazines

By treatment in boiling DMSO, benzothiazolines 1 yield 1,4-benzothiazines 4 in some cases together with benzothiazoles. Two competing pathways, namely oxidative ring-expansion and decomposition of benzothiazoline accounting for the formation of 4 and benzothiazoles, respectively, are suggested.