To a solution of (S)-1 a (290 mg, 1 mmol) in dry T H F (10 mL) at 0 'C was added dropwise nBuLi (0.7 mL of a 1.6 M solution. 1.1 mmol) under argon. The dark solution was stirred at 0 'C for 15 min and 2 h at room temperature. The mixture was cooled to 0 C and iodomethane (120 pL, 2 mniol) was injected. The reaction mixture was stirred at room temperature for 1 h. then quenched with water, and extracted with diethyl ether. Pure 1 I (270 mg, 80%) was isolated as an orange solid after flash chromatography on silica (cyc1ohexane:EtOAc 1 :I) and recrystallized from cyclohexane ([?I,, = +274 (c = 1.5. CHCI,). m.p. = 104 ~ I06 'C). 2a: (R)-1 b (87% a(,) ([XI,, = -257 (c = 0.46. CHCI,) was prepared in 75% yield according to ref. [5] but with a limited amount of ferrocenyllithium (1.Oequiv) at -35 C in order to prevent the in situ racemization of 1 b (P. Diter. unpublished results). (R)-1 b was recrystallized from hexane/cyclohexane ( 3 : l ) until the specific rotation (IllD = -295 (c = 0.3. CHCI,)) was constant.
To a solution of (R)-1 b (648 mg. 2 mmol) in dry T H F (15 mLj was added dropwise LDA (I .2 mL of a 2 M solution, 2.4 mmol) at ~ 78 ' C under argon causing the formation of a light brown precipilate. The suspension was stirred for 15 min at this temperature before treatment with Me,SiCI (380 pL.
3 mmol). After 10 min of stirring at ~ 78 C and warming to room temperature over 1 h. the reaction mixture was quenched with 2 N aqueous sodium hydroxide solution and extracted with diethyl ether The pure sulfoxide 2a was isolated as a bright orange solid (680 mg. 86%) after flash chromatography on silica (cyclohexane,diethyl ether 7:3). ([%ID = +333 (c = 0.88, CHCI,). The enantiomeric excess of 1 b and 2 a ( 2 9 9 % ) was determined by HPLC on a chiral column (OD-H, Daicel Co.).