General procedure for the synthesis of N-Boc-3-hydroxyazetidine from 1-diphenylmethyl-3-hydroxyazetidine and di-tert-butyl dicarbonate: (1) Dissolve 1-diphenylmethyl-3-hydroxyazetidine (10.0 g, 41.8 mmol) in methanol (300 ml), add 10% palladium-carbon catalyst (10.0 g), and carry out the catalytic hydrogenation reaction at room temperature for 3 hours. After completion of the reaction, the catalyst was removed by filtration. To the filtrate was added di-tert-butyl dicarbonate (18.2 g, 83.6 mmol) and stirred at room temperature for 1 hour. After completion of the reaction, the reaction mixture was concentrated under reduced pressure. The residue was purified by silica gel column chromatography with the eluent being hexane: ethyl acetate (1:1→1:2) to afford 1-tert-butoxycarbonyl-3-hydroxyazetidine (7.05 g, 97% yield). (2) To a solution of 1-tert-butoxycarbonyl-3-hydroxyazetidine (2.5 g, 14.4 mmol) in dimethylformamide (125 ml) was added sodium hydride (55% oil dispersion) under ice bath conditions. The ice bath was stirred for 10 minutes followed by 30 minutes at room temperature. Subsequently, iodomethane (1.79 ml, 28.8 mmol) was added to the ice bath and the ice bath was stirred for 10 minutes followed by 1 hour at room temperature. After completion of the reaction, 10% aqueous acetic acid solution was added to the ice bath and stirred for 30 minutes. The reaction mixture was partitioned between ethyl acetate and 10% aqueous sodium chloride solution. The organic layer was washed sequentially with saturated aqueous sodium bicarbonate solution and saturated aqueous sodium chloride solution, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The residue was purified by silica gel column chromatography with hexane:ethyl acetate (2:1) as eluent to afford 1-tert-butoxycarbonyl-3-methoxyazetidine (2.18 g, 81% yield) as a colorless oil.1H-NMR (400 MHz, CDCl3): δ (ppm) 4.16-4.10 (1H, m), 4.09-4.03 (2H, m ), 3.82 (2H, dd, J = 10.2,4.4Hz), 3.28 (3H, s), 1.44 (9H, s).
