Stereochemistry of the fluorination of an alcohol with phenyltetrafluorophosphorane was investigated in the case of steroidal alcohols. 5α-Cholestan-3β-ol and 3α-ol gave 3α- and 3β-fluoro-5α-cholestane, respectively, which suggests that the fluorination proceeded through SN2 mechanism ; while, cholesterol and 3β-acetoxy-5-bromo-5α-cholestane-6β-ol gave fluoro compounds with retention of configuration, which shows that a neighboring group may have participated in stabilizing the carbonium intermediate in special cases. Diphenyltrifluorophosphorane gave similar results.
研究了苯基四
氟磷烷与醇的
氟化反应的立体
化学,特别是在类
固醇醇的情况下。5α-胆烷-3β-醇和3α-醇分别给出了3α-和3β-
氟-5α-胆烷,这表明
氟化反应是通过SN2机制进行的;而
胆固醇和3β-乙酰氧基-5-
溴-5α-胆烷-6β-醇则生成了保持构型的
氟化化合物,这表明在特定情况下,邻近基团可能参与了稳定碳正离子中间体。二苯基三
氟磷烷也得到了类似的结果。