[C:1]([O:5][C:6]([C@H:8]1[CH2:11][C@@H:10]([C:12]([OH:14])=[O:13])[C:9]1([CH3:16])[CH3:15])=[O:7])([CH3:4])([CH3:3])[CH3:2].[CH:17]1[CH:22]=[CH:21][C:20]([CH2:23]Br)=[CH:19][CH:18]=1>CN(C=O)C.C(OCC)(=O)C>[CH3:15][C:9]1([CH3:16])[C@@H:8]([C:6]([O:5][C:1]([CH3:4])([CH3:2])[CH3:3])=[O:7])[CH2:11][C@H:10]1[C:12]([O:14][CH2:23][C:20]1[CH:21]=[CH:22][CH:17]=[CH:18][CH:19]=1)=[O:13]To a stirred solution of (1R,3S)-3-(tert-butoxycarbonyl)-2,2-dimethylcyclobutanecarboxylic acid (step 2, 0.200 g) in DMF (5 ml) Cs2CO3 (0.371 g) was added at about 0° C. under nitrogen atmosphere. After 30 minutes, BnBr (0.11 ml) was added by drop wise to the reaction mixture and stirred for about 2 hours at room temperature. After completion of the reaction (monitored by TLC), the reaction mixture was diluted with ethyl acetate and washed with water. The organic layer was washed with brine, dried over MgSO4 and concentrated under reduced pressure to give crude product which upon column chromatography afforded the title compound (150 mg, 53.9% Yield). 1H NMR (300 MHz, CDCl3): δ 7.37-7.34 (5H, m), 5.12 (2H, d, J=3.9 Hz), 2.80 (1H, t, J=8.1 Hz), 2.768-2.52 (2H, m), 2.0 (1H, m), 1.44 (9H, m), 1.32 (3H, s), 0.953 (3H, s); Mass: [M+Na]+ 341.2 (100%).
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