作者:Xiao-long Qiu、Feng-ling Qing
DOI:10.1039/b206719f
日期:2002.9.11
Both Boc-protected trans- and cis-4-trifluoromethyl prolines were synthesized starting from L-serine simultaneously. In our synthetic route, the key intermediate 4 was obtained through the reaction of Garner's aldehyde 1 with ylide 2 followed by trifluoromethylation with FSO2CF2COOMe–CuI. After hydrogenation followed by reduction of 4, the alcohol 5 was obtained in low diastereoselectivity, however, the two diastereoisomers could be separated easily by flash chromatography in the following steps. The bromide 8b obtained from the alcohol 5 in a straightforward fashion could not afford the desired cyclization product because of the strong electron-withdrawing properties of the trifluoromethyl group and the low ability of bromide as a leaving group. Instead, mesylation of alcohols 12a and 12b followed by treatment with potassium bis(trimethylsilyl)amide (KHMDS) afforded the desired cyclization products 13a and 13b respectively, which were transformed into Boc-protected cis- and trans-4-trifluoromethyl-D-prolines in a straightforward fashion.
同时从L-丝氨酸出发,合成了Boc保护的反式和顺式4-三氟甲基脯氨酸。在我们的合成路线中,关键中间体4是通过加纳醛1与亚胺2反应,然后用FSO2CF2COOMe-CuI进行三氟甲基化反应获得的。在4氢化和还原后,获得了低立体选择性醇5,然而,通过以下步骤的快速色谱法可以很容易地将两种非对映异构体分离。由于三氟甲基基团的强吸电子性和溴化物作为离开基团的低能力,从醇5中直接获得的溴化物8b不能提供所需的环化产物。相反,醇12a和12b的甲磺化,然后用双(三甲基硅基)氨基钾(KHMDS)处理,分别得到了所需的环化产物13a和13b,它们被直接转化为Boc保护的顺式和反式4-三氟甲基-D-脯氨酸。