| 97% | With manganese doped CdS nanoparticles; In water monomer; at 90℃; for 1.5h; | General procedure: In a 50 ml round bottom flask, o-phenylenediamine/aminothiophenol (1 mmol) and aromatic aldehydes (1 mmol) in water (4 ml) were mixed and stirred at 90C. To this, catalyst was added. The progress of the reaction was checked on TLC. After completion, the reaction mixture was cooled at room temperature. Then, it was extracted with ethyl acetate; the organic layer was dried over sodium sulphate and concentrated in a vacuum to afford the crude products. The pure products were obtained by recrystallization from ethanol. |
| 96% | With AlPO4 supported ethylenediamine-chromium(III)-salen complex nanoparticles; air; In ethanol; for 2h;Green chemistry; | General procedure: A mixture of 2-aminothiophenol (1.0 mmol) and arylaldehyde (1.0 mmol) was stirred in 5.0 mL of ethanol in the presence of nanocatalyst (2.0 mol%) at 50 C. After the reaction was completed, the mixture was centrifuged and rinsed with ethanol (3 × 15 mL). The solvent was evaporated to give the crude product, which was purified by silica gel column chromatography with n-hexane/ethyl acetate(10:1) to afford pure 2-arylbenzothiazole. |
| 96% | With Eosin; trypsin (bovine pancreas); In toluene; for 0.166667h;Irradiation; Green chemistry; Enzymatic reaction; | General procedure: 2-aminothiophenol (0.2mmol), p-nitrobenzaldehyde (0.2mmol), Solvent Red 43 1% mol trypsin (10mg), and toluene (2mL) were added to 10mL quartz tube, at 200rpm and at λ=450nm, 20W for 10min. The reaction was completed by filtering the enzyme. The crude products were purified by silica gel column chromatography (200-300 mesh) with an eluent consisting of ethyl acetate-petroleum. Product-contained fractions were combined, concentrated, and dried to give respective product. |
| 95% | With Yb/MCM-41 molecular sieve; In ethanol; at 80℃; for 4h; | A mixture of 2-aminothiophenol (1.1mmol), 4- methylbenzaldehyde (1 mmol of) and Yb / MCM-41 (0.01mmol) added to a round bottom flask was added 5ml of absolute ethanol, is heated with stirring at 80 reflux 4h.Progress of the reaction is detected by TLC, the mixture was filtered after completion of the reaction, the resulting white Yb / MCM-41 molecular sieve catalyst, recycling, and the filtrate solvent was removed by rotary evaporation, and then separated by column chromatography to give the pure product, yield 95 %. |
| 95% | With sulfated tungstate; In neat (no solvent); at 20℃;Sonication; Green chemistry; | General procedure: A mixture of 2-aminothiophenol (2 mmol) and aldehydes (2 mmol), and sulfated tungstate (10 wt%) was sonicated at 20 kHz frequency and 35W power at room temperature for desired times (monitored by TLC). After completion of the reaction as indicated on TLC, the reaction mixture was cooled at room temperature and the crude product was dissolved in ethyl acetate and the catalyst was isolated by simple filtration. It was then dried and reused for another reaction. The product in ethyl acetate was washed with water and excess solvent was removed under reduced pressure. The pure products 2-substituted benzothiazoles were obtained in 88-98% yield and there is no need to purify the products by recrystallization or column chromatography. |
| 94% | With melamine trisulfonic acid; In water monomer; at 70℃; | General procedure: To a mixture of an aromatic aldehyde (1 mmol) ando-aminothiophenol (1 mmol) in 5 mL water, MTSA (0.05mmol) was added and the reaction mixture stirred at 70Cfor 40-65 min. After the reaction was completed, pure products were isolated by filtration and washing with hotwater and ethanol. In some examples the aqueous mixturewas extracted with 10 mL of diethyl ether or ethylacetate and dried over anhydrous Na2SO4, and the solventwas removed under reduced pressure to give thedesired products. The product was analyzed by IR, 1HNMR, 13C NMR, mass and elemental analysis. Furtherpurification of the product was carried out by short columnchromatography on silica gel (hexane/diethyl ether)or crystallization. |
| 93% | With lithium bromide; In ethanol; at 25 - 30℃; for 0.25h;Sonication; | General procedure: Aromatic aldehydes (1.0 mmol), o-aminothiophenol (1.0 mmol), and lithiumbromide (20 mol %) in ethanol (5 mL) were added into a 50-mL round-bottomedflask. The reaction flask was placed in the ultrasonic cleaner bath with the surface ofreactants slightly lower than the water level and irradiated at 25-30 C for theperiod of time indicated in Table 4. The progress of the reaction was monitored byTLC, using petroleum ether/ethyl acetate (8:2) as a solvent system. Aftercompletion of the reaction, the reaction mixture was poured into ice-cold water.The precipitate was filtered off and washed with water, dried, and purified bycrystallization from ethanol as solvent to afford pure product. |
| 93% | With nano titania supported sulfonic acid; In neat (no solvent); at 70℃; for 0.75h;Green chemistry; | General procedure: In a typical experiment, 2-aminothiophenole (1 mmol), aromatic aldehyde (1 mmol),and catalyst (0.099 mmol) in solvent free condition were taken in a 25-mL round-bottomedflask and was stirred at 70 C for an appropriate time. The reaction mixture was cooled,eluted with hot ethanol (5 mL) and was centrifuged and filtrated to collect the formedprecipitate. The crude product was recrystallized from ethanol to yield pure benzothiazolederivatives. |
| 93% | With oxygen; potassium carbonate; at 80℃; for 6h; | General procedure: In a 25 mL round bottomed flask, a mixture of 2-aminophenol,2-aminothiol (1.2 mmol), aldehyde (1 mmol),K2CO3(1.5 mmol), and MNPs-phenanthroline-Pd catalyst(25 mg) was stirred in PEG (3 ml) at 80 C for 6 h. Theprogress of the reaction was monitored by thin-layer chromatography(TLC). After completion of the reaction, catalystwas separated by an external magnet and the reactionmixture was extracted with H2Oand ethyl acetate and driedover anhydrous Na2SO4.After evaporation of the solvent,the desired product was isolated by silica gel flash columnchromatography with a mixture of petroleum ether/ethylacetate as eluent. |
| 92% | With cadmium sulphide; In methanol; at 20℃; for 0.5h;Irradiation;Catalytic behavior; | General procedure: In the experimental procedure for catalytic reaction, amixture of aldehyde (3 mmol), 2-aminothiophenol (3 mmol) and CdSnanosphere (5 mg) was taken in a 100 ml double walled quartz beaker flaskhaving water inlet and outlet to maintain the temperature of the reactionvessel at room temperature in methanol (20 ml). The beaker was exposed tovisible light under stirring condition for the required time period (Table 3).After completion of the reaction (monitored by TLC and GC), methanol wasevaporated by rotary and the product was dissolved in dichloromethane. Thecatalyst was separated from the reaction mixture by centrifugation.Dichloromethane was then evaporated to dryness and the product waspurified by column chromatography using silica gel G60. |
| 92% | With nano-crystalline sulfated zirconia; In ethanol; for 1.41667h;Reflux; | General procedure: In a 50 mL round bottom flask aldehyde (1 mmol) and 1,2-diaminobenzene, 2-aminophenol, or 2-aminothiophenol (1 mmol) were thoroughly mixed in ethanol (10 mL) then catalyst (10 mol%) was added, and the solution was refluxed for appropriate time. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mixture was cooled to room temperature and the resulting solid was collected by filtration and dissolved in 20 mL ethyl acetate. The catalyst was recovered by filtration. After evaporation of the solvent, the resulting solid product was recrystallized from ethanol to obtain pure product. |
| 92% | With tribromide-modified silica-coated magnetic nanoparticles (Fe3O4/SiO2/(CH2)3N+Me3Br3); In neat (no solvent); at 80℃; for 0.283333h;Green chemistry; | General procedure: A stirred solution of the substrate (1 mmol), aryl adehyde (1 mmol),and tribromide-modified silica-coated magnetic nanoparticles (Fe3O4/SiO2/(CH2)3N+Me3Br3-, 0.007 g) was heated 80 C. After completion of the reaction [TLC (AcOEt/hexane 1:3) monitoring], EtOH (10 mL) was added. The catalyst was recovered by an external magnet, and thereaction mixture was poured into ice-water (30 mL). The solid productwas filtered, washed with ice-water, and dried. |
| 92% | With sulfonic-acid-functionalized activated carbon made from matured tea leaf (MTLAC-SA); In ethanol; at 20℃; for 0.75h;Green chemistry;Catalytic behavior; | General procedure: Aldehyde (1 mmol), ortho-phenylenediamine or 2-aminothiophenol (1.1 mmol),synthesized catalyst (10 wt%), and ethanol (3 mL) were mixed and stirred at roomtemperature for appropriate time. After reaction completion as confirmed by thinlayerchromatography (TLC), the usual work-up procedure was carried out and thecrude product was purified using column chromatography to obtain the pureproduct. Both the catalysts were recovered after reaction, washed with ethanol,dried in an oven for about 1 h, and reused for seven cycles successfully. |
| 92% | With oxygen; In neat (no solvent); at 20℃; for 0.416667h; | In around bottom equipped flask 2-mercaptoaniline (1) (1 mmol), substituted aryl/heteroaryl aldehydes 2(a-o) (1 mmol) and CS-SO3H (2 mol %) is stirred at room temperature for 30 min in presence of oxygen balloon. The reaction was monitored by using TLC. Upon completion of the reaction, the reaction mass was quenched to absolute ethanol. The precipitated CS-SO3Hwas filtered and reused for subsequent reactions. The filterate was concentrated and obtained the curde product. Further thecrude product was recrystallized from ethanol and obtained pure products 3(a-o) |
| 92% | With mesoporous Cu(II)-Glycerol-MCM-41 nanocatalyst; In ethanol; at 25℃; for 3.8h; | General procedure: In a 25-mL, round-bottom flask, a mixture of o-aminothiophenol(1.0 mmol), aldehyde (1.0 mmol) and Cu(II)-Glycerol-MCM-41(7 mg) in EtOH (3 mL) was stirred magnetically at room temperaturefor the appropriate time (Table 1). After completion of thereaction, as indicated by TLC, the reaction mixture was filtered toisolate the nanocatalyst and the crude product (filtrate) was purifiedby column chromatography on silica gel or recrystallization intoluene to give the desired products. |
| 92% | | General procedure: All reactions were carried out in an 8 mL vial equipped with a stirring bar. Aldehyde (1 mmol), 2-aminophenol or 2-aminothiophenol(1 mmol), acetonitrile (3 mL), and a base, i.e., K2CO3 or Et3N (2 mmol) were mixed in the vial and stirred at room temperature for 30 min. The vial was then charged with eosin Y (5 mol%) and oxidant (2 mmol), capped, and purged with argon. The stirred reaction mixture was irradiated by 3 W blue LEDs (5 cm away, with a fan to maintain the reaction at room temperature) for 24-36 h. The resulting mixture was transferred to a separatory funnel, partitioned between water (15 mL)and EtOAc (3 × 15 mL). The organic extract was washed with NaHSO310% (30 mL), dried with anhydrous Na2SO4, filtered, concentrated using a rotavap, and analyzed by GCMS using naphthalene as an internal standard. The product was purified by flash column chromatography with hexane/EtOAc mixture as the eluent for NMR characterization. |
| 92% | With ruthenium silicate (Ru/Si, 1:100) zeolite; In neat (no solvent); at 90℃; | General procedure: To the synthesis of 2-arylbenzothiazoles 3 (a-i) from a mixture of 2-aminothiophenol (0.001 mol), benzaldehydes (0.001 mol) and catalytic amount of (0.04 gm) RS-1 under solvent free conditions was refluxed at 90 C for the prescribed time. The reaction progress was monitored by TLC (ethyl acetate: PET ether = 3:7 as eluent), after completion of the reaction, the product and catalyst were separated by simple filtration, and catalyst was easily separated from the reaction mixture. Finally, crude product obtained was crystallized from ethanol to afford desired pure product. The representative compound was characterized by FTIR 1H, 13C NMR and HRMS. |
| 92% | With fluorescein; In methanol; at 20℃;Irradiation; | General procedure: 2-Aminothiophenol derivatives 1 (1 mmol), aromatic aldehyde 2 (1mmol) and fluorescein (10 mol%) were dissolved in 20 mL methanol andplaced in a flat quartz glass jar. The open-air reaction container wasplaced under a 30 W blue LED lamp. After completion of the reaction(monitored by TLC analysis), the solvent was removed under reducedpressure. Then, water (20 mL) was added and the mixture was extractedwith ethyl acetate (3 × 20 mL). The combined organic layer was driedover anhydrous Na2SO4 and the solvent was removed in vacuo. Thecrude product was purified via silica gel column chromatography (petroleumether/ethyl acetate rations of 4:1-6:1) to generate the corresponding product 3.2-Phenylbenzothiazole (3a). 92% yield as a white solid |
| 91% | With UiO-66-NH2-TC-Cu; In neat (no solvent); at 20℃; for 0.333333h;Catalytic behavior; | General procedure: A mixture of aldehyde (1mmol), 2-aminothiophenol (1mmol) and UiO-66-NH2-TC-Cu (10mg, containing 0.0032mmol Cu(II)) was stirred at room temperature. The progress of the reaction was monitored by TLC (eluent: n-hexane/EtOAc, 5:1). At the end of the reaction, EtOAc (15mL) was added; the catalyst was filtered and washed with EtOAc (10mL). Concentration of the filtrate and purification of the crude product by recrystallization from n-hexane/EtOAc (10:1) afforded the pure product. |
| 91% | With (N‑[(3‑methoxy‑2‑oxidophenyl)methylidene]pyridine‑3‑carbohydrazonato)‑bis(oxido)‑methoxo‑oxo‑vanadium(V); In ethanol; for 0.0833333h;Sonication; | General procedure: 10 mol% of the catalyst, VOL or MoO2L,was added to an ethanolic solution of aryl aldehydes (1 mmol) and 1,2-phenylenediamine,2-aminophenol, or 2-aminothiophenol(1 mmol). The mixture was subjected to ultrasonic irradiation at room temperature for an appropriate period of time until the reaction was completed, as indicated by TLC (eluentn-hexane: ethyl acetate, 5:2). Then, the reaction mixturewas filtered and the product was finally recrystallized from the ethanol to achieve maximum purity. |
| 90% | With nano-TiO2-SO3H; at 70℃; for 0.75h; | General procedure: In a typical experiment, aromatic aldehyde (1mmol), 2-aminothiophenol(1mmol) and n-TSA (0.032g) under solvent free conditions were taken in a 25mL round bottomed flask and were stirred at 70C for an appropriate time. The reaction mixture was cooled, eluted with hot ethanol (5mL) and was filtrated to collect the formed precipitate. The crude product was recrystallized from ethanol to yield pure benzothiazole derivatives. |
| 90% | With Ag2CO3/celite; In ethanol; at 70℃; for 3h; | General procedure: To a mixture of 1,2-phenylenediamines (1.0 mmol) andaldehydes (1.1 mmol) in ethanol, 25 mol % of Ag2CO3/Celite (3 mL) was added. The resulting mixture was stirredat 70 C for 3 h. After this time, the reaction mixture wasdiluted with ethanol (50 mL) and the catalyst was separatedby filtration. Water was then added to the organic layer, andthe products were filtered and washed with water. All of theproducts are known compounds and characterized easily bycomparison with melting point, IR, [1-6] H NMR spectraldata reported in literature. |
| 90% | With ionic liquid immobilized on silica-coated cobalt-ferrite magnetic nanoparticles; In neat (no solvent); at 70℃; for 0.166667h; | General procedure: CoFe2O4SiO2PAF-IL (20 mg) was added to the mixtureof aromatic aldehyde (1 mmol), o-phenylenediamine(1 mmol, 0.11 g), or 2-aminobenzenethiol (1 mmol, 0.125 g)and heated in solvent-free conditions at 70 C for an appropriatetime. After completion, the resulting mixture wasdiluted with hot ethanol (10 mL), and the catalyst was easilyseparated using an external magnet. Finally, the gainedprecipitate was recrystallized in ethanol to afford the pure product. |
| 89% | With uronium nitrate; In neat (no solvent); at 20℃; for 0.0333333h; | General procedure: 2-Aminothiophenol 1 (2.0 mmol) and carbaldehyde 2 (2.0 mmol) were mixed in a conical flask and NH2CONH2.HNO3 (1.5 wt % of aldehydes) was added to it. This mixture was shaken at room temperature. An instant exothermic reaction occurred with completion of reaction (TLC) and gave yellowish orange solid that was directly chromatographed over silica gel column to afford pure 2-aryl/heteroaryl/styryl/alkylbenzothiazole 3 (Table 3). The structures of synthesized compounds were confirmed by the overlapping 1H, 13C NMR and melting points data. The spectral data of some of the synthesised compounds are given below. |
| 88% | With DL-10-camphorsulphonic acid; In ethanol; water monomer; at 20℃; for 1h;Green chemistry; | General procedure: In a dry screw-cap test tube a magnetic stir bar, aromatic aldehydes (1a-1k; 1 mmol), 2-aminothiophenol (2; 1 mmol), 4 mL aqueous ethanol and a catalytic amount of camphor sulfonic acid (20 mol%) were taken sequentially. On a magnetic stirrer, the reaction mixture was then stirred vigorously at room temperature and it was monitored by TLC. After completion of the reaction, solid 2-arylbenzothiazoles (3a-3k) were isolated pure just by simple filtration and washing the crude products with aqueous ethanol (H2O:EtOH = 1:2) subsequently. By repeating the above mentioned procedure, 2-arylbenzimidazoles (5a-5c) were also synthesized from the reaction of aromatic aldehydes (1c; 1 mmol) and o-phenylenediamine (4; 1 mmol) in the presence of a catalytic amount of camphor sulfonic acid as catalyst under the same optimized conditions. The structures of all the synthesized compounds were determined by the detail spectral analysis including 1H NMR, 13C NMR and HRMS spectroscopy. |
| 87% | With copper (II) bromide; In toluene; at 111℃; for 0.583333h; | General procedure for the synthesis 3-5: The catalyst (100 mg) was added to a mixture of aldehyde 2 (1.1 mmol) and o-phenylenediamine 1a, o-aminophenol 1b or o-aminothiophenol 1c (1.0 mmol). The mixture was stirred at 111 C in the presence of 5 mL toluene. Progress of the reaction was monitored by TLC (n-hexane/EtOAc 2:1). After complete conversion, the reaction mixture was filtered, the catalyst was washed, and the solvent was removed under reduced pressure. The crude material was purified by column chromatography or recrystallization to afford the pure product 3, 4 or 5. |
| 87% | With 1-butyl-3-methylimidazolium tetrachloroferrate(III); In ethanol; for 1.33333h;Reflux; | General procedure: A mixture of 2-aminobenzenethiol or 2-aminobenzenthiol (1 mmol), aryl aldehyde (1mmol), [bmim][FeCl4] (0.5 mmol) and ethanol (5 mL)was placed in a round bottom flask and refluxed forthe given times recorded in Table 2. After completionof the reaction observed by TLC (using n-hexane/ethylacetate (7:3) as eluent), the mixture was cooledto room temperature, the precipitate was filtered andwashed with water for several times. The resultantproduct purified by column chromatography andcharacterized by comparison of their physical data with benzimidazole or benzthiazole derivativesreported in literature. |
| 87% | With fluorophosphoric acid; In ethanol; at 20℃; for 2.5h; | General procedure: A mixture of o-substituted amino-aromatics 1(i-iii) (0.1 mol)and aldehydes 2(a-u) (0.1 mol) was added in 100 mL round bottom flask containing ethanol (10 mL). A known catalyticamount of fluorophosphoric acid was added in the abovesolution. The resulting reaction mixture was stirred at roomtemperature for an appropriate time. After completion ofthe reaction, it was monitored by TLC (hexane/ethyl acetate90:10). The work-up was performed for the reaction mixtureby diluting it with ice cold water and extracting it by ethylacetate. The organic layer was separately collected andevaporated under vacuum on rotary evaporator to obtainsolid crude product. The obtained solid product was further purified by recrystallization with hot ethanol and by passing sample through a short column of silica gel wheneverrequired. |
| 86% | With nitric acid supported on a silica gel; at 20℃; | General procedure: To a mixture of 2-aminothiophenol 1 (2.0 mmol) and aryl/heteroaryl/styryl/alkylaldehyde 2 (2.0 mmol) in a vial was added SiO2-HNO3 (2 wt% to the aldehyde)and shaken at room temperature. Instantly, an exothermic reaction occurred withcompletion of the reaction (TLC) and the reaction mixture became a yellowishorangesolid that was directly chromatographed over a silica gel column to affordpure 2-aryl/heteroaryl/styryl/alkylbenzothiazole 3 (Table 3). |
| 85.7% | With oxygen; at 25 - 30℃; for 1h;Sonication; | General procedure: Aromatic aldehydes (2, 1.0 mmol), o-aminothiophenol (1, 1.0 mmol), FeCl3/Montmorillonite K-10 (160 mg, 0.1 mmol, based on FeCl3) and absolute methanol (5 mL) were added into a 25 mL conical flask. The reaction flask was placed in the ultrasonic cleaner bath, where the surface of reactants was slightly lower than the water level and irradiated at 25-30 C for the period of time (sonication was continued until aromatic aldehydes disappeared as indicated by TLC) as indicated in Tables 1-4 . After completion of the reaction, the reaction mixture was dissolved in ethyl acetate and FeCl3/Montmorillonite K-10 was filtered off. The filtrate was concentrated and purified by silica-gel column chromatography (200-300 mesh) using petroleum ether or the mixture of petroleum ether and ethyl acetate as eluent to give a light yellow crystalline solid. All of the products described herein were previously reported in the literatures [16-35]. The authenticity of the products was established by spectroscopic data and by comparing their melting points with literature values. white crystals, IR (KBr, cm-1): 3058, 3023, 1608, 1484, 1457, 1434, 1312, 1286, 1253, 1227, 1122, 959, 834, 817, 761; 1H NMR: δH 8.10 (d, J = 7.9 Hz, 1H, ArH), 8.02 (d, J = 8.2 Hz, 2H, ArH), 7.91 (d, J = 8.0 Hz, 1H, ArH), 7.50-7.53 (m, 1H, ArH), 7.38-7.41 (m, 1H, ArH), 7.32 (d, J = 7.9 Hz, 2H, ArH), 2.45 (s, 3H, CH3); 13C NMR: δC 168.3, 154.2, 141.5, 134.9, 131.0, 129.7, 127.5, 125.0, 126.3, 123.1, 121.6, 21.5; m/z (ESI): 226 [M+H]+. |
| 85% | With ammonium nickel sulphate hexahydrate; at 25℃; for 1.75h;Sonication; Green chemistry; | General procedure: o-amino thiophenol (1mmol), aromatic aldehyde (1.1mmol) andwater (10mL) were mixed in 25mL single neck round bottom flask, andto this Ammonium Nickel Sulphate (10 mol %) was added. The reactionmixture was sonicated at room temperature (250C) for the appropriate time(Table 2, entries 13-25), and the progress of reaction was monitored by TLC.After completion of reaction, the mixture was extracted with ethyl acetate(2×10mL). The combined organic layer was dried over anhydrous Na2SO4 andevaporated under reduced pressure; the crude material was purified by columnchromatography over silica gel to afford products 4a-4m with high purity. |
| 85% | With air; In dimethyl sulfoxide; at 60℃; for 6h; | General procedure: 2-Aminothiophenol (0.5 mmol; 1.0 equiv) and aromatic aldehydes (0.6 mmol; 1.2 equiv)were dissolved in DMSO (3 mL). Then, the reaction mixture was stirred at 60 C for 6 h. Afterthe reactionH2O was added to the mixture. The mixture was extracted with AcOEt (20 mL x 3).The combined organic layers were then washed with saturated aq. NaCl (30 mL). The solutionwas dried with anhydrous Na2SO4, filtered, and concentrated in vacuo. The crude residue waspurified with silica gel chromatography (AcOEt- PE130) to give pure product. |
| 85% | With ZnCl2/SiO2; In neat (no solvent); at 50℃; for 0.75h; | General procedure: To a stirred mixture of aldehyde, (10mmol), and 2-ainothiophenol (10 mmol), Silzic (0.1 g, 10 mol%) was added and the mixture was allowed to stir at 50 0C for the total recorded time. After the completion (the reaction was monitoredby TLC pet.ether-EtOAc (8:2)) of the reaction, EtOAc(20 mL) was added to the reaction mixture. Then, the solidwas filtered off. Removal of solvent under reduced pressureprovided the crude products with high purity, if required;recrystallization was performed from CH2Cl2 in some cases.The 2-aryl benzothiazoles are known compounds and allspectroscopic data were in agreement with literature reports[44, 49] (Table 5). |
| 83.9% | With montmorillonite K-10; air; In ethanol; at 20℃; for 12h; | General procedure: Aldehyde (2, 1.0 mmol) and o-aminothiophenol (1, 1.0 mmol) were mixed inabsolute ethanol (10 mL) in a 50-mL three-necked flask equipped with a watercooledcondenser and a gas inlet, as reported elsewhere [45]. The solution wasstirred at room temperature, then montmorillonite K-10 (25 mg) was added. Air wasbubbled continuously through the reaction system, at a speed of 60 bubbles perminute on average, by means of a small air pump. After completion of the reaction(monitored by TLC) the catalyst was recovered by filtration and washed with EtOH.The filtrate was concentrated and purified by short column chromatography on silicagel, with petroleum ether or a mixture of petroleum ether and ethyl acetate aseluent, to give the pure product. The products (3a-r) are all known compounds andwere identified by 1H NMR spectroscopy, by comparison of their melting pointswith those reported in the literature, and by comparison of their TLC Rf values withthose of standards. |
| 83% | With 3-(2,4,6-trimethyl-3,5-bis((1,2-methyl-1H-imidazoliumbromide-3-yl)methyl)benzyl)-1,2-methyl-1H-imidazoium bromide; mesoporous silica; In neat (no solvent); at 100℃; for 0.266667h; | General procedure: Required equivalents as mentioned for conventional method exceptsolvent and 5 g of silica gel (80-120 mesh) were taken and mixed andfinely grinded using mortar and pestle. The reaction mixture is kept inMuffle furnace at 100 C for completion. The progress of the reactionis monitored by TLC. |
| 82% | With tetraethylammonium L-prolinate; at 90℃; for 6h; | General procedure: [N2222][AA] catalysts (0.4 mmol), benzaldehydes (1.98 mmol), o-aminothiophenol (2.28 mmol), and solvent (5 ml) were added into a round-bottom flask (25 ml) with a magnetic stirrer and condenser. The temperature of the reaction mixture was controlled by using a temperature controller with an accuracy of ±0.01 C. Then, the reactor was heated to the designated temperature in an oil bath with stirring. After the reaction was completed, deionized water (10 ml) was added to the reaction mixture. The products were precipitated out, and the aqueous phase containing [N2222][AA] ILs was isolated simply by filtration, thus were recovered and reused in the next run after heat treatment to remove water under vacuum at 90 C for 12 h.The pure products were obtained by recrystallization with EL/water or silica gel column chromatography. |
| 82% | With H3PO4/TiO2-ZrO2(1/1)-cetyl pyridinium bromide; at 20℃; for 0.25h; | General procedure: A mixture of 2-aminothiophenol (1 mmol, 0.995 g), aldehyde (1 mmol), and H3PO4-TiO2- ZrO2 (1/1) (40 mg, 30 wt%H3PO4) were added in a beaker and the reaction mixture was mixed properly with the help of glass rod under solvent-free condition at room temperature. The progress of the reaction was monitored by TLC (ethylacetate-hexane, 4:6). After completion of the reaction, the reaction mixture was dispersed in ethyl acetate (5 mL) and filtered and the catalyst was washed several times with ethyl acetate and acetone. Then, the filtrate was evaporated under reduced pressure to isolate a solid residue and recrystallized from hot ethanol (10 mL) to afford the corresponding products. All of the 2-arylbenzothiazole products were characterized by IR, 1H NMR, 13C NMR, and mass spectroscopy and identified by comparison of their physical and spectral data with those of authentic samples.[34,35] |
| 82% | With [Fe3O4/SiO2/(CH2)3NPC-SO3H]Cl magnetic nanoparticles; In water monomer; at 70℃; for 0.75h; | General procedure: A mixture of an aldehyde (1 mmol) with 2-aminothiophenol (1 mmol) and the catalytic amount of [MNP-PNPC-SO 3 H]Cl (30 mg) was magnetically stirred in water (5 mL) at 70C for the appropriate time (Table 1). Upon completion of the reaction, as indicated by TLC (n-hexane-ethyl acetate, 5 : 1), the catalyst was separated by an external magnet. After evaporation of the solvent, the crude product was recrystallized from ethanol-water (10 : 1) to give the corresponding pure compound. |
| 81% | With yttrium(III) chloride; In ethanol; for 0.5h;Reflux; Green chemistry; | General procedure: YCl3(0.0098 g, 0.05 mmol) were dissolved in 10mL EtOH and stirred until the soliddissolved completely in refluxing, then 2-aminobenzenethiols 1a (0.118 mL, 1.1mmol) and benzaldehyde 2a (0.101 ml, 1.0 mmol) was added into thereaction mixture. After 30min, TLC showed the reaction to be complete. Thereaction mixture was cooled to r.t., and then evaporated in vacuum. The productpurified by column chromatography (PE-EtOAc= 20:1) to give white solid 3a(0.2092 g, 99%) |
| 80% | With nano silica-supported boron trifluoride (nano BF3/SiO2); In ethanol; at 20℃; for 0.416667h; | General procedure: To a mixture of 2-aminothiophenol (1 mmol, 0.995 g) and aldehyde (1 mmol) in ethanol (10 ml), nano BF3/SiO2 (0.05 g, 25 mol% BF3) was added in a beaker and the reaction mixture was mixed properly with the help of a glass rod and stirred in ambient temperature for the time indicated in Table 3. The progress of the reaction was monitored by TLC (ethyl acetate:hexane, 6:4), after completion of the reaction the solvent was removed under reduced pressure, then the mixture was cooled and dichloromethane (15 ml) was added to the mixture and filtered to remove the catalyst. Then the filtrate was evaporated under reduced pressure to isolate a solid residue, and recrystallized from ethanol (10 ml) to afford the corresponding products and the catalyst residue was washed with acetone and reused. All of the 2-arylbenzothiazole products were identified by physical and spectroscopic data as follows. |
| 79% | With iron(III) trichloride hexahydrate; In water monomer; at 70℃; for 1h;Sonication; Green chemistry; | General procedure: General procedure: 2-Aminothiophenol 1 (1 mmol), adehyde 2 (1.2 mmol), FeCl3•6H2O (0.02 mmol), were addedin water (5 mL) and heated at 70 C in the presence of air under ultrasound (using a laboratory ultrasonic bath SONOREX SUPER RK 510H model producing irradiationof 35 KHz) for 1 h. |
| 79% | With oxygen; C31H25BNO; In dimethyl sulfoxide; for 10h;Irradiation; | In this example, 2-(p-tolyl)benzo[d]thiazolethiazole was prepared in milligram level. The quartz reaction tube was filled with oxygen first, and then 2-aminobenzenethiol (37.56mg, 0.3mmol, 1.0equiv) was added. 4-methylbenzaldehyde (54.07mg, 0.45mmol, 1.5equiv), PC (1.3mg, 0.003mmol, 1.0mol%), dimethyl sulfoxide (2.0mL) were added to the quartz reaction tube, at 10w light intensity 455nm The reaction was carried out at 25C for 10 hours under the irradiation of a blue LDE lamp with a wavelength. At the end of the reaction, the reaction mixture was filtered, washed with ethyl acetate, and the solvent was removed by rotary evaporation, and then purified by silica gel column chromatography (the specification of silica gel is 200-300 mesh, the mass ratio of silica gel to the product to be purified is 200:1, and the eluent is petroleum ether. A mixture with a volume ratio of 10:1 and ethyl acetate) to obtain the target product 2-(p-tolyl)benzo[d]thiazole with a yield of 79% (53.40 mg). |
| 78% | | General procedure: The mixture of o-aminophenthiols 4a, aldehydes 2 (0.5mmol, 1 equiv) in 5mL 1,4-dioxane was stirred at 100C with oil bath for 1h. [BMIm]2[WO4] (0.1mmol, 53mg, 0.2 equiv) was added to reaction mixture for further 4h at 100C in the open air. The reaction was monitored by TLC. After completion of the reaction, the resulting solution was cooled to room temperature and pour it into the water (30mL) followed by extraction with ethyl acetate (10mL×3). The combined organic phase was washed with water three times. The solvent was removed by vacuum evaporation. The pure products were obtained by silica gel column chromatography. |
| 70% | With potassium carbonate; 3-butyl-1-methyl-1H-imidazol-3-ium iodide; In o-dimethylbenzene; para-xylene; 1,3-dimethylbenzene; at 120℃; for 10h;Green chemistry; | General procedure: Into a 15x150 mm glass tube were layered o-amino phenol (1a-1d)/benzenethiol (4) (1 mmol) and corresponding aldehyde (1 mmol), xylene (3 mL; mixture of o, m, p-xylene), 0.25 mmol K2CO3 (34 mg) and NHC precursor G (0.1 mmol, 26 mg), the mixture was lowered under pre-heated oil bath, the mixture was stirred vigorously for 10 hours under air atmosphere. After reaction, the mixture was diluted with ethyl acetate, filtrated, the organic solution was concentrated under vacuum, the residue was applied on silica gel column chromatography, which afforded the corresponding oxidative cyclization product 3aa-3dd; 5a-5n. |
| 68% | With graphene oxide; In water monomer; at 60℃; for 7h;Green chemistry; | General procedure: A mixture of aldehyde (1mmol) and o-phenylenediamine 1a (1mmol, 108.1 mg) in water (1 mL) were added to dispersed solution of GO (100 wt%, 108.7 mg) in water (2 mL) and the reaction mixture was stirred at 60 C forappropriate time (Table 2). After completion of the reaction(monitored by TLC using n-hexane/EtOAc 9:1 as eluent), theGO was separated by filtration and the solution was extractedwith ethyl acetate (2 5 mL). The GO was washed with warmethanol (about 75 C, 5 10 mL) and then organic layers(EtOAc and ethanol) were combined and dried over anhydroussodium sulfate. The solvents were removed under reducedpressure and the residue left out was purified by chromatographyon a short column of silica gel eluted with n-hexane/ethyl acetate (9:1) to give the corresponding benzimidazoles 2in 78-95%yield (Table 2). |
| 68.89% | With 4-methyl-2-pentanone; In methanol; for 8h;Reflux; | 2-Aminothiophenol (0.03 mol, 3.76 g) was added to 4-methylbenzaldehyde (0.03 mol, 3.60 g) and 4-methylpent-3-en-2-one (0.03 mol, 2.94 g) in methanol, heated under refluxfor 8 h, and the reaction mixture allowed to stand overnightin the fume hood. The product was recrystallized andobtained as a brown solid from ethanol: acetone (1:1).Yield = 68.89%, Mp = 46-47 C, 1H NMR (DMSO-d6-400MHz) δ 8.11 (d, J = 8.0 Hz, 1H), 8.06 (m, J = 8.4 Hz, 1H),7.99 (d, J = 8.0 Hz, 02H), 7.54 (t, J = 7.6 Hz, 1H), 7.56 (t,J = 7.2, 7.6 Hz, 2H), 7.37 (t, J = 8, 10 Hz, 2H), 2.38 (s,3H). 13C NMR (DMSO-d6-100 MHz) δ 167.7 (C = N),153.8 (C), 148.3 (C), 142.0 (C), 138.0 (C), 134.8 (CH),130.8 (CH), 130.4 (CH), 129.4 (CH), 127.6 (CH), 127.1(CH), 126.0 (CH), 123.2 (123.3), 122.7 (CH), 21.3 (CH3).IR (νmax, cm-1): 3349 (N-H), 3055 (C-H), 2914 (C-H),1685 (C = N), 1610 (C = N), 1581 (C = C), 1500 (C = C),1472 (C-N). Anal. calcd. for C14H11NS: C, 74.63; H, 4.92;S, 14.23; N, 6.22. Found: C, 74.51; H, 4.84; S, 14.17; N,6.32. GC-MS (m/z, M+): Found for C14H11NS = 225.17,Expected mass = 225.31. |
| 60% | With methanol; carbon dioxide; oxygen; at 70℃; under 24752.5 Torr; for 12h;Autoclave; Sealed tube; | General procedure: A stainless-steel autoclave reactor equipped with a magnetic stirrer was charged with 2-aminothiophenol (1 mmol), aromatic aldehydes (1.2 mmol) and methanol (2 mL). Then the stainless-steel autoclave was sealed and pressurized with 0.3 MPa of O2 and 3 MPa of CO2 after air was replaced at ambient temperature. And then it was heated and stirred at 70 C for 12 h. When the reaction was completed, it was cooled down to room temperature and the excessive gas was released slowly. Subsequently, the excessive aromatic aldehydes were removed by saturated sodium bisulfite aqueous solution and extracted with ethyl acetate (3x30 mL). The combined organic layers were dried over anhydrous MgSO4 and evaporated under reduced pressure. The desired products were obtained in moderate to excellent yields after purification by column chromatography on silica gel using petroleum ether/ethyl acetate as the eluent. All the desired products were identified through comparisons with the corresponding 1H NMR, 13C NMR and MS data reported in the literatures. The Supplemental Materials contains sample 1H and 13C NMR spectra of the products, 3, and the full characterization data (Figures S1-S32). |
| With disodium metabisulfite; In N,N-dimethyl-formamide; for 2h;Reflux; | In a typical procedure, benzothiazoles 1-26 were synthesized by mixing together commercially available 2-aminothiophenol (3.12 mmol) and different aromatic aldehydes (3.16 mmol) in N,N-dimethylformamide (DMF) 10 mL, sodium metabisulfite Na2S2O5 (0.61 g) was added to a stirring mixture. The reaction mixture was refluxed for 2 h and the progress of the reaction was monitored by TLC. After completion of the reaction, mixture was allowed to cool to room temperature, addition of water (30 mL), product which precipitated as a solid, after filtration afforded the benzothiazole derivatives 1-26 in high yields. Recrystallization from methanol afforded pure product. |
| With disodium metabisulfite; In N,N-dimethyl-formamide; for 2h;Reflux; | General procedure: In a typical reaction, benzothiazoles 1-26 were re-synthesized by dissolving 2-aminothiophenol (3.12mmol) and different aromatic aldehydes (3.16mmol) in DMF (10mL). Sodium metabisulfite (Na2S2O5, 0.61g) was also added to the above-mentioned solution with continuous stirring. The resulting reaction mixture was refluxed for 2h and the progress of the reaction was monitored by TLC analysis. After completion of the reaction, it was allowed to cool to room temperature and water (30mL) was added. The solid precipitated benzothiazoles (1-26) were collected on a filter and obtained in high yields. Recrystallization from methanol yielded pure products and their physical and spectroscopic data matched satisfactorily with previously reported literature values [21]. |
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