Reaction Steps
To a stirred mixture of (3S*,4R*)-1-tert-Butyldimethylsilyl-3-[2-(4-methoxybenzoyloxy)methyl-2-propenyl]-4-phenyl-2-azetidinone (18.74 g, 41.5 mmol), pH7 phosphate buffer (15.0 ml), and CH2Cl2 (250 ml) was added 2,3-dichloro-5.6-dicyano-1,4-benzoquinone (DDQ, 15.1 g, 66.4 mmol) portionwise at room temperature; on the addition, the reaction mixture became dark green, and then red solids precipitated with stirring. (In the course of addition, a slight heat evolution was observed.) The stirring was continued at room temperature for two hours, the reaction being monitored by TLC[Merck Kieselgel 60, n-hexane-AcOEt (3:1)]. sat. NaHCO3 aq. solution (80.0 ml) was added to quench the reaction, wherein gas evolution was observed. After Celite was added, the mixture was filtered through a pad of Celite, and the filter cake was washed with CH2Cl2. The combined filtrate and CH2Cl2 washings were washed with sat. NaHCO3 aq. solution (×2), and dried (MgSO4). The combined aqueous washings were filtered through a pad of Celite, and the filter cake was washed with CH2Cl2. From the combined filtrate and washings, the CH2Cl2 layer was separated, and the aqueous layer was extracted with CH2Cl2 (100 ml×3). The combined CH2Cl2 layer and washings were dried (MgSO4). The CH2Cl2 solution dried were combined, treated with activated charcoal, and concentrated in vacuo to give an orange oil (22.1 g). This was flash chromatographed over SiO2 (Merck Kieselgel 60, 200 g). Elution with n-hexane-AcOEt (15:1/5:1/3:1) gave title compound (11.18 g, 81.2%) as a viscous pale yellow oil. IRmax (film): 3420(s), 1750(s), 1733(s), 1718(s), 1705(s), 1650(m), 1040(s), 900(s), 775(s) 700(s) cm-1 ; 1H-NMR δ: 7.43-7.25(m, 5H), 5.04(br.s, 1H), 4.82(br.s, 1H), 4.20(d, J=2.2 Hz, 1H), 4.06(br.s, 2H), 3.26(ddd, J=8.2, 7.0, 2.2 Hz, 1H), 2.67(dd, J=15.2, 7.0 Hz, 1H), 2.54(dd, J=15.2, 8.2 Hz, 1H), 2.42(br.s, 1H, OH), 0.92(s, 9H), 0.21(s, 3H), -0.19(s, 3H) ppm.
