| 87% |
With 3-(2,4,6-trimethyl-3,5-bis((1,2-methyl-1H-imidazoliumbromide-3-yl)methyl)benzyl)-1,2-methyl-1H-imidazoium bromide; silica gel; In neat (no solvent); at 100℃; for 0.233333h; |
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. |
| 85% |
In methanol; glycerol; at 90℃; for 4h; |
General procedure: To a stirred solution of 2-aminophenol (0.1 g, 0.92 mmol) in methanol (1 mL), glycerol (5 mL) was added and the reaction mixture was heated to 90 C, followed by addition of benzaldehyde (0.1 g, 0.92 mmol). The reaction mixture was stirred vigorously at 90 C. The progress of reaction was monitored by TLC. After completion of reaction, the product was isolated as above procedure. |
| 85% |
With nano-crystalline sulfated zirconia; In ethanol; for 1h;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. |
| 85% |
With trichloro(trifluoromethanesulfonato)titanium(IV); In ethanol; at 20℃; for 1.66667h; |
General procedure: General procedure: To a stirred solution of o-phenylenediamine or o-aminophenol (1 mmol) and aldehyde (1 mmol) in ethanol (5mL) at room temperature was added TiCl3OTf (10 mol%). The reaction mixture was stirred at ambient temperature for the specified time (see Table 2), when the reaction was complete (TLC), the mixture was filtered to separate the catalyst and the filtrate was concentrated under reduced pressure. Then cold water (10mL) was added to precipitate the product. This was collected by filtration and recrystallised from ethanol-water. IR and 1H NMR data of selected compounds are given below. |
| 80% |
With potassium cyanide; In N,N-dimethyl-formamide; at 20℃; for 6h; |
A mixture of o-aminophenol (1, 2 mmol), benzaldehyde (2, 2 mmol) and KCN (2 mmol) in DMF (5 mL) was stirred at room temperature, the progress of the reaction was monitored using thin layer chromatography. Once the reaction was complete, the reaction mixture was diluted with 30 mL of water and extracted twice with ethyl acetate (30 mL), the solvent was removed under reduced pressure. The obtained solid was then recrystalized from a boiling mixture of ethanol/water 50-50, giving the pure compound. |
| 80% |
With potassium permanganate; acetic acid; In neat (no solvent); at 20℃; for 0.166667h; |
General procedure: In a mortar, aldehyde (1 mmol), 2-aminophenol (1 mmol),KMnO4 (3.4 mmol) and HOAc (0.08 mL) were chargedand ground for 10 min. The progress of reaction was monitoredby TLC (ethyl acetate:n-hexane, 20:80). Then, acetone(5 mL) was added to the mortar and filtered the mixture.By adding water to filtrate, 2-aryl-1,3-benzoxazolewas appeared as a pure solid. |
| 76% |
|
General procedure: The mixture of o-aminophenols 1 (0.6mmol, 1.2 equiv), aldehydes 2 (0.5mmol, 1 equiv) in 1,4-dioxane (5mL) 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 3 were obtained by silica gel column chromatography. |
| 71% |
With silica chloride; In neat (no solvent); at 120℃; for 4h; |
General procedure: To the flask containing a mixture of substituted benzaldehyde (1mmole) and 2-aminophenol (1mmole) was added silica chloride(1 eq) and was heated on a sand bath at 120 C, TLC was taken afterevery 1 h. After 4 h, TLC showed appearance of new spot. The productwas isolated by first separating out the catalyst by filtration using organicsolvent; the organic layer was dried using anhydrous sodiumsulfate and evaporated under vacuum. The solid thus obtained was recrystallized using petroleum ether and its % yield and melting pointswere determined. The results are tabulated in Table 1 and Table 2. |
| 68% |
With potassium carbonate; 1-methyl-3-(n-butyl)imidazolium iodide; In o-xylene; para-xylene; m-xylene; 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. |
| 65.12% |
With toluene-4-sulfonic acid; In toluene; for 16h;Heating / reflux; |
Synthesis of 2-(4-bromophenyl)benzo[d]oxazole2-aminophenol 7.86 g (72 mmole), 4-bromobenzaldehyde 16 g (87 mmole), and 2.8 g of PTSA (14 mmole) was stirred in 150 ml of Toluene, the reaction mixture was then heated to reflux for 16 hours, after cooling, the reaction mixture was extracted with water, and then the organic layer was evaporated to dry, the residue was then recrystallized with acetone to get 12.85 g of product (yield=65.12%). |
|
In ethanol; at 20℃; for 6h; |
Add 10.0 g (0.092 mol) of 2-aminophenol, 16.9 g (0.092 mol) of 4-bromobenzaldehyde and 114 mL of ethanol, and stir at room temperature for 6 hours. After the reaction was completed, the solvent was distilled off under reduced pressure and dried to obtain a Crude intermediate (1). The purification process is omitted and the next reaction proceeds. |
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