Imidazole → 4-[2-(Tert-butyldimethylsilanyloxy)-2-methylpropoxy]-3,5-dimethylbenzonitrile

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Reaction Steps

To a solution of 4-hydroxy-3,5-dimethylbenzonitrile (2.00 g, 13.5 mmol) and 1-chloro-2-methyl propan-2-ol (8.85 g, 81.5 mmol) in ethanol (50 mL) was added potassium carbonate (7.5 g, 54 mmol) and water (5 mL). The reaction mixture was stirred at reflux for 24 hours. Cooled to room temperature. The precipitated solid was filtered off and washed with water. The solid was dissolved in ethyl acetate (100 mL), washed with water (50 mL), brine (50 mL) and dried over anhydrous Na2SO4. Removal of solvent gave 4-(2-hydroxy-2-methylpropoxy)-3,5-dimethyl benzonitrile (2.9 g, 97%) as a white solid. To a solution of 4-(2-hydroxy-2-methylpropoxy) 3,5-dimethyl benzonitrile (2.90 g, 13.2 mmol) in anhydrous DMF (20 mL) was added imidazole (2.7 g, 40 mmol) and tert-butyldimethylsilylchloride (2.19 g, 14.6 mmol). The reaction mixture was stirred at room temperature under nitrogen for 3 days. Water (200 mL) was added and the mixture was extracted with ethyl acetate (200 mL). The organic layer was washed with water (2×100 mL) and brine (100 mL), and dried over anhydrous Na2SO4. The solvent was removed under reduced pressure and the crude compound was purified by column chromatography (Silica Gel 230-400 mesh; 10% ethyl acetate in hexanes as eluent) to give 4[2-(tert-butyldimethylsilanyloxy)-2-methylpropoxy]-3,5-dimethylbenzonitrile (2.24 g, 54%). n-Butyl lithium (6.2 mL, 6.6 mmol, 1.6 M solution in hexanes) was added to a solution of 2,4-dimethoxy-6-N-dimethylbenzamide (0.9 g, 4.3 mmol) in anhydrous THF (10 mL) dropwise at −10° C. over a period of 10 min under nitrogen. The stirring was continued at 0° C. for 1 hour. The reaction mixture was cooled to −50° C. A solution of 4-[2-(tert-butyldimethylsilanyloxy)-2-methylpropoxy]-3,5-dimethylbenzonitrile (1.58 g, 4.73 mmol) in anhydrous THF (5 mL) was quickly added. The cooling bath was removed and the reaction mixture was allowed to warm to room temperature. The stirring was continued at room temperature for 1 hour. Aqueous ammonium chloride solution (10 mL) was added. Ethyl acetate (100 mL) was added. The organic layer was separated, washed with water (10 mL) and dried (Na2SO4). The solvent was removed under reduced pressure and the crude compound was purified by column chromatography (Silica Gel 230-400 mesh; 0-5% methanol in CH2Cl2 as eluent) to give 3-{4-[2-(tert-butyldimethylsilanyloxy)-2-methylpropoxy]-3,5-dimethylphenyl}-6,8-dimethoxy-2H-isoquinolin-1-one (0.82 g, 37%) of as white solid. The above compound (0.42 g, 0.82 mmol) was dissolved in anhydrous THF (20 mL). Tetrabutyl ammonium fluoride (4.1 mL, 11.0M solution in THF) was added at 0° C. The reaction mixture was stirred at 0° C. for 10 min, then at room temperature for 2 h and then stirred at 70° C. for 24 hours. The mixture was cooled to room temperature. Saturated aqueous ammonium chloride (30 mL) was added. The organic phase was separated, washed with water, brine and dried over anhydrous Na2SO4. The solvent was removed under reduced pressure. The crude product was purified by column chromatography (Silica Gel 230-400 mesh; 0-4% methanol in CH2Cl2 as eluent) to give 3-(4-(2-hydroxy-2-methylpropoxy)-3,5-dimethylphenyl)-6,8-dimethoxyisoquinolin-1(2H)one (0.15 g, 46%) as a white solid. MS (ES) m/z: 398.96 (M+1); MP 252-254° C.

Provenance & Evidence