A cooled (−78° C.) solution of commercially available 5-bromo-2,3-dihydrobenzo[b][1,4]dioxine (500 mg; 2.32 mmol) in anh. THF (5 ml), under nitrogen, was treated dropwise with a solution of 1.6 M n-BuLi in hexanes. The resulting solution was further stirred at −78° C. for 10 min. A solution of methyl 5-((tert-butylsulfinyl)imino)pentanoate (542 mg; 2.32 mmol) in anh. THF (2 ml) was added to the cooled reaction mixture, and stirring at −78° C. was continued for 10 min., and then at −20° C. for 2 h. The resulting reaction mixture was treated successively with aq. sat. NH4Cl (15 ml), Et2O (30 ml) and water (15 ml). The separated organic layer was then washed with brine (15 ml), dried over anh. MgSO4, filtered, and concentrated to dryness under reduced pressure. Purification by FC (DCM/MeOH=20/1) afforded methyl 5-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-5-(1,1-dimethylethylsulfinamido)-pentanoate as a yellow oil. LC-MS (conditions A): tR=0.73 min.; [M+H]+: 369.73 g/mol.
