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Step a. tert-FJutyl 3-hydroxy-3-methylazetidine-l- carboxylate. Methyl magnesium bromide (3M in diethyl ether; 2.92 mL, 8.76 mmol) was added portionwise into a cold (0 °C) solution of tert-butyl 3-oxoazetidine-l-carboxylate (0.5 g, 2.92 mmol) and anhydrous THF (3 mL). The mixture was allowed to come to room temperature and stirred for 3 hours and carefully quenched with aqueous ammonium chloride. The mixture was extracted with ethyl acetate, washed with brine and dried over anhydrous MgS04. The solvents were removed under vacuum and the residue was purified on silica gel (Biotage; eluting solvents hexanes: EtOAc 1/1 ratio) to afford tert-butyl 3- hydroxy-3-methylazetidine-l-carboxylate as oil (480 mg, 87percent yield): XH NMR (500MHz, CDCk) δ ppm 3.87 (d, J= 9.0 Hz, 2H), 3.82 (d, J= 9.0, 2H), 2.46 (s, 1H), 1.51 (s, 3H), 1.44 (s, 9H).
84%
Stage #1: at 0 - 20℃; for 19.75 h; Stage #2: With ammonium chloride In diethyl ether; water at 20℃;
Step B: Preparation of 3-hvdroxy-3-methyl-azetidine-1-carboxylic acid tert-butyl ester.; A solution of 1 -Boc-azetidin-3-one (3.5 g, 20 mmol) in 50 ml_ anh Et2O was cooled to 0 0C and 3M MeMgBr in Et2O (10 ml_, 30 mmol) was added dropwise over 1 h. After 45 min, the reaction was allowed to warm to rt and stir an additional for 18h. Then Vi sat'd NH4CI (aq.) was added and the mixture extracted with EtOAc (2x). The combined organic layers were dried and the resulting semisolid was purified by RP HPLC (Agilent) to give the title compound as a white solid (3.2 g, 84percent). 1H NMR (CDCI3): 3.84 (q, J = 9.2 Hz, 4H), 1.97 (bs, 1 H), 1.52 (s, 3H), 1.44 (m, 9H).
78.3%
at 0℃; for 1 h; Inert atmosphere
In an oven dried flask, tert-butyl 3-oxoazetidine-l-carboxylate (1.01 g,5.900 mmol) was dissolved in diethyl ether (0.2 M) and place under an atmosphere of N2. The reaction mixture was cooled to 0°C and treated dropwise with methylmagnesium bromide (2.07 mL, 6.195 mmol, 3.0 M). The reaction mixture was stirred at 0°C for 1 hour then quenched by pouring onto ice. The mixture was extracted with diethyl ether, washed with water and brine, dried over Na2S04, filtered, and concentrated in vacuo to provide tert- butyl 3-hydroxy-3-methylazetidine-l-carboxylate (865.3 mg, 4.621 mmol, 78.3percent yield).
430 mg
at 20 - 35℃; for 1 h;
Methyl magnesium bromide (3.0M in Diethyl ether) (1.5 mL, 4.5 mmol) was added to cold (-10° C.) solution of tert-butyl 3-oxoazetidine-1-carboxylate (650 mg, 3.8 mmol) in THF (10 mL) and stirring was continued at 20-35° C. for 1 h. After which the reaction mixture was quenched with saturated aqueous NH4Cl solution and extracted with ethylacetate. The organic layer separated was washed with water, dried over anhydrous sodium sulphate and concentrated under reduced pressure to afford the residue. The residue was purified by column chromatography (using 60-120 silica gel and 50percent EtOAc in Hexane as eluent) to afford 430 mg of the title compound. 1H NMR (400 MHz, DMSO) δ ppm 5.56 (1H, s), 3.7-3.5 (4H, m), 1.4 (9H, s), 1.3 (3H, s).
430 mg
at -10 - 35℃; for 1 h;
Methyl magnesium bromide (3.0M in Diethyl ether) (1.5 mL, 4.5 mmol) was added to cold (?10° C.) solution of tert-butyl 3-oxoazetidine-1-carboxylate (650 mg, 3.8 mmol) in THF (10 mL) and stifling was continued at 20-35° C. for 1 h. After which the reaction mixture was quenched with saturated aqueous NH4Cl solution and extracted with ethylacetate. The organic layer separated was washed with water, dried over anhydrous sodium sulphate and concentrated under reduced pressure to afford the residue. The residue was purified by column chromatography (using 60-120 silica gel and 50percent EtOAc in Hexane as eluent) to afford 430 mg of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 5.56 (1H, s), 3.7-3.5 (4H, m), 1.4 (9H, s), 1.3 (3H, s) ppm.
Stage #1: at 0℃; for 1 h; Stage #2: With water; ammonium chloride In tetrahydrofuran
Step 1 In a dry round-bottomed flask, 1-Boc-3-azetidinone (0.70 g, 4.1 mmol) was dissolved in THF (20 mL). The solution was cooled to 0° C. and methylmagnesium chloride (3.0 M solution in THF, 2.0 mL, 6.0 mmol) was added dropwise. The reaction mixture was stirred at 0° C. for 1 h. The reaction mixture was quenched with 10 mL saturated NH4Cl, diluted with 5 mL water and extracted with 100 mL EtOAc (2*). The combined organic layers were washed with 10 mL water and 10 mL brine then combined, dried over sodium sulfate, filtered and concentrated to afford 757 mg (99percent) of 3-hydroxy-3-methyl-azetidine-1-carboxylic acid tert-butyl ester as an off-white solid.
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