The general procedure for the synthesis of (R)-tert-butyl sulfinic acid thio-tert-butyl ester from tert-butyl disulfide was as follows: first, ligand L1 was prepared by reacting an equal amount of (1S,2R)-serpentinic acid trimethylsilyl ether with 3,5-dimethylsalicylaldehyde (for details of the preparation, see: Org. Synth. 2005, 82, 157). Subsequently, ligand L1 (5.0 mmol) was dissolved with VO(acac)2 (1.27 g, 4.8 mmol) in acetone and the reaction was stirred for 1 hour. After the color of the system darkened, the progress of the reaction was monitored by TLC. Next, tert-butyl disulfide (171.2 g, 0.96 mol) was dissolved in 190 mL of acetone and the reaction temperature was controlled at -5°C to 0°C. At this temperature, 25% hydrogen peroxide (1.0 mol) was added slowly dropwise, and the dropwise process took about 20-22 hours. After completion of the reaction, the reaction temperature was maintained until the ratio of feedstock to product reached 90:1, which was taken as the end point of the reaction. Throughout the process, the reaction temperature should not exceed 35°C. At the end of the reaction, the solvent was removed by distillation under reduced pressure. To the residue was added 350 mL of 2-methyltetrahydrofuran, the organic layer was washed with saturated brine, dried over anhydrous magnesium sulfate, and the solution was tested by filtration. The yield of (R)-tert-butylsulfinyl tert-butyl thioester was 93% (173.5 g, 0.89 mol) with an ee value of 96.2%.
