To an ice-cold stirred solution of tert-butyl 3-hydroxyazetidine-1-carboxylate (2.20 g, 12.7 mmol) and triethylamine (1.54 g, 15.2 mmol) in THF (60.0 mL) was added methanesulfonyl chloride (1.60 g, 14.0 mmol) and the resulting reaction mixture was warmed to room temperature. After 2 h the reaction mixture was filtered and filtrate concentrated under reduced pressure. The residue was dissolved in toluene (30.0 mL), added to a stirred solution of 80% 2-tert-butylthiophenol (2.12 g, 10.2 mmol), tetrabutylammonium bromide (0.41 g, 1.27 mmol) and sodium hydroxide (4.80 ml of 8.0 M solution in water, 38.4 mmol) in toluene (30.0 mL) and the resulting reaction mixture was heated at 100° C. for 3 h. Then, the reaction mixture was cooled to room temperature, diluted with ethyl acetate and separated. The organic layer was washed with water, saturated sodium chloride, dried (Na2SO4), filtered and concentrated under reduced pressure. The residue was purified by flash column chromatography (silica gel, 95:5 to 80:20 heptane/ethyl acetate) provided tert-butyl 3-(2-tert-butylphenylthio)azetidine-1-carboxylate (1.80 g, 55%) as a pale yellow oil.
