Palladium-catalyzed synthesis of 2-substituted benzothiazoles via a C-H functionalization/intramolecular C-S bond formation process

Catalytic synthesis of 2-substituted benzothiazoles from thiobenzanilides was achieved in the presence of a palladium catalyst through C-H functionalization/C-S bond formation. This method features the use of a novel catalytic system consisting of 10 mol % of Pd(II), 50 mol % of Cu(I), and 2 equiv of Bu4NBr that produced variously substituted benzothiazoles in high yields with good functional group tolerance.     

Na2S2O4-Mediated Cyclocondensations of 2,2'-Disulfanediyldianilines with Aldehydes: A Facile and Inexpensive Method for the Synthesis of 2-Substituted Benzothiazoles

A facile and inexpensive method for the synthesis of 2‐substituted benzothiazoles has been developed by Na₂S₂O₄‐mediated cyclocondensations of 2,2′‐disulfanediyldianilines with aldehydes. In the presence of Na₂S₂O₄ and 4 Å molecular sieves, a variety of 2‐substituted benzothiazoles were obtained from the reaction of 2,2′‐disulfanediyldianilines with aldehydes in moderate to high yields.     

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.     

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.     

Synthesis of some substituted imidazo [5, 1-b] benzothiazoles

Cyclization of formylated and acetylated -substituted 2-aminomethylbenzothiazoles with phosphorus oxychloride gives 3-substituted imidazo [5, 1-b] benzothiazoles, and 3-substituted 1-methylimidazo [5, 1-b] benzothiazoles. Treatment of 2-benzothiazolyl-4-pyridylaminomethane with formic acid gives 3-(4-pyridyl) imidazo [5, 1-b] benzothiazole. 1-Mercapto-3-phenylimidazo [5, 1-b] benzothiazole is converted into 3-phenylimidazo [5, 1-b] benzothiazole by elimination of the mercapto group.     

Synthesis of 2-(imidazolylamino)benzothiazoles

Treatment of derivatives of 5-phenylthioureido-3H-imidazole-4-carboxylic acid with bromine afforded 2-(imidazolylamino)benzothiazoles.     

Convenient Solid-phase Synthesis of Benzothiazole Derivatives

Resin-bound cyclic malonic ester 1 reacted with aryl isothiocynate, then was treated with bromine, followed by cleavage from the resin under perchloric acid to give benzothiazoles 4.     

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.     

Yttrium-catalyzed heterocyclic formation via aerobic oxygenation: A green approach to benzothiazoles

The YCl₃-catalyzed aerobic oxidative cyclization reaction for the synthesis of benzothiazoles has been developed.This method provides a practical,effective and green synthetic approach to benzothiazoles which are important units in many biologically active compounds.     

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.     

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 and the influence of intramolecular H-bonding in NMR spectra of novel analogs of dendrodoine: Diaminothiazoloylbenzothiazoles

2-(4-Amino-2-arylaminothiazol-5-oyl)benzothiazoles, as the novel analogs of the cytotoxic marine alkaloid dendrodoine, are synthesized and characterized by elemental analysis, IR, NMR and mass spectral data. The thiourea derivatives provide four ring atoms for the thiazole ring construction and thus act as [C–N–C–S] synthons. The remaining carbon of the thiazole is sourced from 2-(2-bromoacetyl)benzothiazoles. This [4+1] heterocyclization reaction is adopted for the synthesis of novel benzothiazole derivatives. The presence of two signals in the ¹H NMR spectrum arising from the NH₂ hydrogens shows that the two hydrogens are not exchanging rapidly on the chemical shift time scale and they are in two different chemical environments due to H-bonding.     

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.     

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。      

6-Substituted 2-(2-benzothiazolyl) [1, 2, 3] benzotriazol-1-oxides and the kinetics of their formation

6-Substituted 2-(2-benzothiazolyl) [1, 2, 3] benzotriazol-1-oxides were prepared by a base catalyzed cyclization reaction of 2-(4-substituted 2-nitrophenylhydrazino) benzothiazoles. Influence of substitution in position 4 on the cyclization reaction rate was followed and correlated with Hammett constants.     

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.     

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.     

Base-catalyzed hydrogen-deuterium exchange in some 5-substituted benzothiazoles and in thiazolo-[4,5-c]pyridine. effect of substituents and polar effects of the aza group

The rates of base-catalyzed hydrogen-deuterium exchange at C-2 in some 5-substituted benzothiazoles and in thiazolo[4,5-c]pyridine were studied. Transmission through the thiazole ring of the effects of substituents in the benzothiazoles and of the polar effects of the aza group in the thiazolopyridine, was assessed from these data.     

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.     

High resolution mass spectrometry.—II Some substituted benzothiazoles

The mass spectra of nineteen substituted benzothiazoles have been recorded and the identity of the various ions in the mass spectra has been established by high resulution (accurate) mass measurement. Deuterium labelling has been used to elucidate the fragmentation processes of these compounds. The parent compound of the series, benzothiazole, exhibits the loss of hydrogen cyanide and carbon monosulphide from the parent ion as the most important decomposition pathways. The hydrogen atom concerned in the loss of hydrogen cyanide is shown to originate from the 2-position of benzothiazole, while in 2-substituted benzothiazoles, different mechanisms are apparent for the loss of hydrogen cyanide, and these are clarified by deuterium labelling. Some substituted benzothiazoles can lose sulphur from their molecular ions, a process which does not occur in benzothiazole itself. The substituted benzothiazoles undergo many other types of fragmentations, in some cases retaining the substituent, and in other cases losing it prior to collapse of the thiazole ring.