C[Si](C)(C)[O:3][C:4]1[C@@H:9]([O:10][CH3:11])[CH2:8][CH2:7][CH2:6][CH:5]=1.C([Mg]Br)C.C(O[C@H:22]1[NH:25][C:24](=[O:26])[C@@H:23]1[C@H:27]([O:29][Si:30]([C:33]([CH3:36])([CH3:35])[CH3:34])([CH3:32])[CH3:31])[CH3:28])(=O)C.Cl>O1CCCC1.C(OCCCC)(=O)C>[Si:30]([O:29][C@@H:27]([C@@H:23]1[C@@H:22]([C@H:5]2[CH2:6][CH2:7][CH2:8][C@H:9]([O:10][CH3:11])[C:4]2=[O:3])[NH:25][C:24]1=[O:26])[CH3:28])([C:33]([CH3:36])([CH3:34])[CH3:35])([CH3:32])[CH3:31]To a solution of 1-trimethylsilyloxy-6-(S)-methoxy-1-cyclohexene (800 mg, 4 mmol) in tetrahydrofuran (5 ml), a tetrahydrofuran solution containing 1 mol/liter of ethylmagnesium bromide was added and stirred at room temperature for 3 days. This mixture was then cooled to 0° C., and a solution of (3R,4R)-4-acetoxy-3-[(1R)-1-tert-butyldimethylsilyloxyethyl)-2-azetidinone (861 mg, 3 mmol) in tetrahydrofuran (5 ml) was added dropwise to the mixture and stirred at 0° C. for 1 hour. The resultant mixture was subjected to addition of 2N hydrochloric acid and extraction with butyl acetate. The organic phase was washed with a saturated sodium hydrogencarbonate solution and water, and concentrated under a reduced pressure to obtain a crude product of (3S,4R)-3-[(R)-1-((tert-butyldimethylsilyl)oxy)ethyl]-4-[(1R,3S)-3-methoxy-2-oxocyclohexyl]azetidin-2-one. The crude product contained 170 mg of the objective β-isomer. The yield was 16%, and the β:α ratio was 90:10.
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