[O:1]=[O+][O-].[CH2:4]([O:7][CH:8]1[CH2:25][CH2:24][C:11]2([CH2:16][CH2:15][N:14]([C:17]([O:19][C:20]([CH3:23])([CH3:22])[CH3:21])=[O:18])[CH2:13][CH2:12]2)[CH2:10][CH2:9]1)[CH:5]=C.CSC>CO>[O:1]=[CH:5][CH2:4][O:7][CH:8]1[CH2:9][CH2:10][C:11]2([CH2:12][CH2:13][N:14]([C:17]([O:19][C:20]([CH3:22])([CH3:23])[CH3:21])=[O:18])[CH2:15][CH2:16]2)[CH2:24][CH2:25]1O3 gas was passed through a stirred solution of tert-butyl 9-(allyloxy)-3-azaspiro[5.5]undecane-3-carboxylate (6.47 mmol, 1.0 eq.) in MeOH (40 ml) for 45 min at −78° C. Dimethylsulfide (77.64 mmol, 12.0 eq.) was added dropwise to the reaction mixture at 0° C. and it was stirred for 30 min at 25° C. The reaction mixture was concentrated under reduced pressure to yield the crude product as a light yellow oil which was used in next step without further purification. Yield: 99%
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