Peroxide-mediated oxidative coupling of primary alcohols and disulfides: Synthesis of 2-substituted benzothiazoles

A peroxide-mediated protocol for the synthesis of 2-substituted benzothiazoles was developed, starting from bis(o-aminophenyl) disulfides and primary alcohols. Eleven differently 2-substituted benzothiazoles were prepared in moderate to excellent yields using di-tert-butyl peroxide (DTBP) as an oxidant.     

A novel reaction between benzothiazoles and diaroylacetylenes in the presence of Meldrum’s acid: ring expansion of benzothiazoles to functionalized 1,4-benzothiazines

A novel and efficient ring expansion of benzothiazoles to functionalized 1,4-benzothiazines is described. The reactive 1:1 zwitterionic intermediates formed by addition of benzothiazoles to diaroylacetylenes were trapped with Meldrum’s acid under mild reaction conditions to produce 2-[2-hydroxy-2-aryl-2H-1,4-benzothiazin-3(4H)-yliden]-1-aryl-1-ethanones in excellent yields.     

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.     

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.     

Iodine-mediated cyclisation of thiobenzamides to produce benzothiazoles and benzoxazoles

Synthesis of benzothiazoles by reaction of iodine with thiobenzamides, which do not possess an ortho alkoxy or ester group, is described. The unlikely synthesis of benzoxazoles from reaction of 2-alkoxythiobenzamides with iodine is also reported.     

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.     

Direct C–H amination of benzothiazoles by magnetically recyclable CuFe2O4 nanoparticles under ligand-free conditions

A simple and highly practical method for the synthesis of 2-N-substituted benzothiazoles has been developed by using nano copper ferrite as a magnetically separable, recyclable catalyst. The present tandem process allows to get access to a wide range of 2-N-substituted benzothiazoles in good to excellent yields by the reaction of benzothiazole with nitrogen nucleophiles in the presence of Cs₂CO₃ as a base. The nano CuFe₂O₄ could be recovered and reused with no significant loss of catalytic activity.     

One-pot approach for the synthesis of 2-aryl benzothiazoles via a two-component coupling of gem-dibromomethylarenes and o-aminothiophenols

One-pot synthesis of 2-aryl benzothiazoles from gem-dibromomethylarenes using 2-aminoarylthiols is described. Benzothiazoles were obtained in high chemical yields under mild conditions. This transformation would facilitate synthesis by short reaction times, large-scale synthesis, easy and quick isolation of the products, which are the main advantages of this procedure.     

CuO nano-particles supported on silica,a new catalyst for facile synthesis of benzimidazoles,benzothiazoles and benzoxazoles

A facile synthetic route for benzimidazoles, benzothiazoles and benzoxazoles comprising the reaction of corresponding o-phenylenediamine, o-aminothiophenol and o-aminophenol with various aldehydes using silica supported nano-copper (II) oxide as a catalyst has been described. The catalyst exhibited a clean reaction profile with excellent yields in a short reaction time. The catalyst can be recycled effectively after use.     

Alkylation reactions of benzothiazoles with N,N-dimethylamides catalyzed by the two-component system under visible light

Eosin Y/K₂S₂O₈ catalyzed C2-alkylation reactions of benzothiazoles with N,N-dimethylamides under visible light have been developed. The reactions completed smoothly in the presence of Eosin Y as the photocatalyst and K₂S₂O₈ as the oxidant under solvent-free conditions in open air. This green and simple method provides an alternative route for the synthesis of C2-alkylation of benzothiazoles and tolerates a number of functional groups to afford moderate to excellent yields.     

Synthesis of 2-benzylimidazo[2,1-b][1,3]benzothiazoles through palladium-catalyzed heteroannulation of acetylenic compounds

The reaction of 2-imino-3-(2-propynyl)-1,3-benzothiazole with various iodobenzenes in the presence of a palladium catalyst leads to the production of 2-benzylimidazo[2,1-b][1,3]benzothiazoles.     

An efficient and reusable heterogeneous catalyst Animal Bone Meal for facile synthesis of benzimidazoles, benzoxazoles, and benzothiazoles

A library of benzimidazoles, benzoxazoles, and benzothiazoles was efficiently synthesized by condensation of o-phenylenediamine, o-aminophenol, and o-aminothiophenol respectively with aromatic aldehydes in the presence of catalytic amounts of Animal Bone Meal (ABM) and Lewis acids doped ABMs. Reactions were conducted under reflux conditions in air. The remarkable features of this new protocol are high conversion, short reaction times, and cleaner reaction profiles, straightforward procedure, and reduction in catalyst toxicity.     

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 pyrazole- and thiazole-annulated 3-R-1,5-dinitro-3-azabicyclo[3.3.1]nonanes

The previously unknown 3-R-1,5-dinitro-3-azabicyclo[3.3.1]nonanes fused to the pyrazole or thiazole rings were synthesized by the reductive cyclization of m-dinitroindazoles and benzothiazoles. The method is based on the reduction of carbon-carbon bonds in the benzene ring, which are activated by the meta-nitro groups, with NaBH₄ followed by the Mannich reaction with formaldehyde and primary amines.     

A stereoselective three-component reaction: The facile synthesis of fluorinated tetrahydropyrimido[1,2-b]benzothiazoles

A one-pot, catalyst- and solvent-free approach has been developed for the stereoselective synthesis of fluorinated tetrahydropyrimido[1,2-b]benzothiazoles. The three-component condensation reaction of an aldehyde and a trifluoromethyl ??-dicarbonyl compound in the presence of 2-aminobenzothizole occurs in high yields at 90 °C.     

Base-catalyzed hydrogen-deuterium exchange in some 5- and 6-substituted benzothiazoles. Activity of the sulphur and nitrogen heteroatoms in the transmission of the substituent effects

The rates of base-catalyzed hydrogen-deuterium exchange at C-2 in some 6-substituted benzothiazoles were studied and compared with the analogous values pertinent to some 5-substituted benzothiazoles, reported in a previous paper. The simple Hammett equation was found not to allow a good interpretation of the experimental data. However, a good agreement was obtained by the application of the Hammett-Jaffé equations. From these calculations, it was concluded that the sulphur and the nitrogen heteroatoms of the thiazole ring have, in these reactions, a very similar activity in the transmission of the substituent effects from the benzo ring at C-2 of the thiazole ring. Therefore, while in other reactions only the nitrogen heteroatom is active, in these reactions a considerable stabilization of the α-carbanion is clearly shown also by the sulphur heteroatom.     

An efficient copper(II)-catalyzed synthesis of benzothiazoles through intramolecular coupling-cyclization of N-(2-chlorophenyl)benzothioamides

A wide range of 2-aryl or 2-alkyl-substituted benzothiazoles are synthesized through intramolecular C_(aryl)-S bond forming-cyclization using copper(II)-BINAM-catalyzed coupling of less reactive N-(2-chlorophenyl)benzo or alkylthioamide under mild reaction conditions (82 °C).     

Iridium-catalyzed intramolecular CN and CO/S cross-coupling reactions: Preparation of benzoazole derivatives

The irdium-catalyzed intramolecular arylcarbon-hetero cross-coupling reactions with o-haloarylamides or o-haloarylamidine have been effectively achieved using KOAc and just 1 mol% catalyst. The [Ir(cod)Cl]₂ was proved to be more potential for smoothly assembling functional structures benzimidazoles, benzoxazoles and benzothiazoles, which was superior to Cu- and Pd-catalyzed systems. Simultaneously, a concise and efficient synthesis of tafamidis was developed in 5-g scale.     

Green and Highly Efficient Synthesis of Mono‐ and Bis‐Benzothiazoles in the Presence of Fe(SD)3 under Ultrasound Irradiation

A convenient, practical, green, and environmentally friendly method was developed for the synthesis of benzothiazoles from 2‐aminothiophenol and various aldehydes. Bis‐benzothiazoles were synthesized in high yield under mild reaction conditions. Products were obtained in the presence of in situ prepared Fe(SD )₃ [iron(III ) dodecyl sulfate] as a combined Lewis acid–surfactant catalyst (LASC ) in water under ultrasound irradiation.     

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.