Br[C:2]1([CH2:10][C:11]([O:13][Si:14]([C:17]([CH3:20])([CH3:19])[CH3:18])([CH3:16])[CH3:15])=[O:12])[C:6](=O)[O:5][C:4]([CH3:9])([CH3:8])[O:3]1.N12CCCN=C1CCCCC2>C(Cl)(Cl)(Cl)Cl.O1CCCC1>[CH3:8][C:4]1([CH3:9])[O:5][CH2:6]/[C:2](=[CH:10]/[C:11]([O:13][Si:14]([C:17]([CH3:20])([CH3:19])[CH3:18])([CH3:15])[CH3:16])=[O:12])/[O:3]1The solution of crude 4-bromo-2,2-dimethyl-5-oxo-1,3-dioxolane-4-acetic acid, tert-butyldimethylsilyl ester (72.4 mmol) in carbon tetrachloride (˜220 ml) was cooled to 0-5° C. and treated dropwise over 10 minutes and under good stirring with a solution of 1,8-diazabicyclo (5,4,0) undec-7-ene (12.1 g, 79.6 mmol) in dry tetrahydrofuran (125 ml). A heavy precipitate was formed which gradually became a granular solid. After 1 h, the solid obtained was filtered and washed with a small amount of tetrahydrofuran. The filtrate was concentrated under reduced pressure to give a light orange oil which was used as such for the next step.
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