合成路线1

Preparation of fragment (VIII) is illustrated in Scheme 24509401a. Aldol condensation of aldehyde (I) with (R)-4-benzyl-3-propionyl-2-oxazolidinone (II) mediated by dibutylboron triflate gives the syn aldol adduct (III). This is converted to the Weinreb amide (IV) by treatment with N,O-dimethyl hydroxylamine in the presence of trimethylaluminium. After silylation of the secondary hydroxyl group of (IV), the resultant bis-silyl ether (V) is selectively desilylated at the primary hydroxyl group with p-toluenesulfonic acid and tetrabutylammonium bisulfate, to afford alcohol (VI). Dess-Martin oxidation of (VI) gives the aldehyde (VII), which is then subjected to Corey-Fuchs olefination with CBr4 and PPh3 to produce the gem-dibromo olefin (VIII)