A convenient preparation of 2-substituted benzothiazoles

Abstract

Light-induced substitution reactions of aryl fluorides have been recently reviewed.l Bryce-Smith and co-workers2 have recently observed cine-substitution by nucleophilic substitution of fluorobenzene and difluorobenzenes with primary and secondary amines and found evidence for the additionelimination mechanism. Irradiation of solutions of hexafluorobenzene in cyclohexane and cyclooctane gives hydrogen fluoride and a complex mixture containing cyclohexylpentafluorobenzene and other radical coupling products.3

Synthesis of Poly(benzothiazole) by Direct Polycondensation of Dicarboxylic Acids with 2,5-Diamino-1,4-benzenedithiol Dihydrochloride Using Phosphorus Pentoxide/Methanesulfonic Acid as Condensing Agent and Solvent

“…2-Substituted benzothiazoles (3) have been prepared directly from o-aminobenzenethiol (1) and carboxylic acids by treatment with PPMA at room temperature for 1 h and warming about 70-90oC for 10 h. 10 In the present study, the reactions of 1 and aromatic car-…”

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“…Treatment of 2-aminothiophenol and substituted aromatic acids in presence of Polyphosphoric acid provides a good method to synthesize 2-substituted benzothiazoles and gives a good yield [14][15][16] . Further aryl substituted 2-phenyl benzothiazoles (1.5) and L-lysyl and l-alanyl amide prodrugs of 2-(4-aminophenyl) benzothiazole (1.6) were found to possess exquisitely potent anti-proliferative activity [29][30] .…”

“…The classical method involves condensation of o-aminothiophenols with substituted aldehydes [8][9][10][11][12][13][14] , acyl chlorides, carboxylic acids [15][16] or esters, nitriles 17 . Other most commonly used methods include Pd/Cu/Mn/chloranil catalyzed cyclization of ohalothioformanilides [18][19][20][21][22] .…”

Cerium‐catalyzed tandem synthesis of 2‐substituted benzothiazoles in PEG

“…[4 -6] Recently, Choo et al reported that 2-substituted benzothiazoles exhibited topoisomerase II inhibitory activities. [7] One of the most common methods for the synthesis of benzothiazoles involves the direct condensation of the 2-aminothiophenol with aldehydes, carboxylic acids or its derivatives in the presence of various promoting agents, such as polyphosphoric acid (PPA), [8] polyphosphate ester, [9] a mixture of methanesulfonic acid and phosphorous pentoxide, [10] FeCl 3 , [11] Sc(OTf) 3 , [12] TCCA, [13] ionic liquid under microwave irradiation, [14] molecular iodine, [15] acetic acid under microwave irradiation [16] and silica sulfuric acid under microwave irradiation. [17] Some other general methods include palladium-catalyzed intramolecular cyclization of o-bromophenylthioureas, [18] Suzuki biaryl coupling of 2-bromobenzothiazole with arylboronic acids, [19] coupling of benzothiazoles with aryl bromides, [20] microwave-mediated reaction of 2-aminothiophenol with β-chlorocinnamaldehydes, [21] the reaction between thiophenols and aromatic nitriles, [22] and the intramolecular cyclization of thiobenzamides via aryl radical cations as reactive intermediates.…”