A stereoselective total synthesis of (±)-cephalotaxine (1) has been achieved. Palladium-catalyzed [3+2] cycloaddition of 2-(trimethylsilylmethyl)-2-propenyl acetate to the nitrostyrene 7 gave the methylenecyclopentane 6, which was converted into the α-sulfinylacetamide 19. Treatment of 19 either with trifluoroacetic anhydride in dichloromethane at room temperature or with p-toluenesulfonic acid in boiling 1, 2-dichloroethane gave the benzazepinone 20 in good yield, and this was transformed to (±)-1 via Hanaoka's key intermediate 4.
已实现(±)-cephalotaxine (1)的立体选择性全合成。利用
钯催化的[3+2]环加成反应,将2-(三甲基
硅烷基甲基)-2-
丙烯基
乙酸酯与
硝基乙烯7反应,得到
亚甲基环戊烷6,其随后转化为α-亚砜乙酰胺19。在室温下,将19与
二氯甲烷中的
三氟乙酸酐或与沸腾的
1,2-二氯乙烷中的
对甲苯磺酸反应,均能以良好产率获得苯并氮杂卓酮20,并通过Hanaoka的关键中间体4将其转化为(±)-1。