【作者】 罗钒；

【导师】 龚跃法；

【作者基本信息】 华中科技大学 ， 无机化学， 2011， 博士

【摘要】 氟代醇是碳氢键上氢原子被氟原子取代的一类醇。氟代醇作为一类重要的含氟中间体,因其特异的性质已越来越受到大家的关注。但是,关于单氟取代的,特别是氟原子直接连在手性中心的氟代伯醇的合成方法却并不多见。因此,单氟代手性伯醇的合成是一个值得探究的课题。本论文主要研究了面包酵母不对称还原2-氟烯丙醇类化合物的反应,并通过该反应高对映选择性地合成了手性含氟伯醇。为了更好地理解面包酵母还原取代烯丙醇类化合物的历程,论文第二章主要研究了面包酵母还原2-烷基-3-芳基烯丙醇的反应。首先通过对面包酵母还原反应条件的筛选,获得了最佳的反应体系,包括pH值、反应时间、底物的浓度和面包酵母的用量。随后,我们考察了2-位取代基以及3-位芳基对面包酵母还原反应的影响。通过系统的分析,发现随着2-位取代基的体积的增大,反应的转化率快速地下降。同时还发现当3-位芳基由苯基换为呋喃基后,反应的转化率有明显的提高。由此可见,给电子取代基可以使得碳碳双键上的电子云密度增大,从而提高面包酵母还原取代烯丙醇的转化率。论文第三章主要探讨了面包酵母还原2-氟取代肉桂醇的反应。研究发现,由于氟的原子半经与氢非常接近,并且氟原子直接与碳碳双键相连时诱导与共轭效应的共同作用并不会明显降低碳碳双键上的电子云密度,2-氟肉桂醇反应48小时后,基本上可以等量的转化为饱和醇,产物的ee值为81%。在相同的反应条件下,2-溴肉桂醇的转化率仅为5%,说明溴原子较大的体积及吸电子性质不利于反应的进行。苯环上的取代基对2-氟取代肉桂醇反应速率的影响也很明显,吸电子取代基使得苯环上的电子云密度降低,反应的转化率也随之降低。经面包酵母还原48小时后,3-(4-甲氧基苯基)-2-氟-2-烯丙醇和3-(4-氟苯基)-2-氟-2-烯丙醇基本上可以完全转化为相应的饱和醇,产物的ee值分别能够达到92%和82%,而3-(4-氯苯基)-2-氟-2-烯丙醇的转化率仅为27%。根据旋光度和核磁数据结果表明,面包酵母还原2-氟取代肉桂醇的产物均为(S)-构型,与文献报道的立体化学一致。为了扩大面包酵母还原底物的适用性,论文第四章主要研究了2-氟烯丙醇类化合物碳碳双键的构型对还原反应的影响和一系列(Z)-3-烷基-2-氟-2-丙烯醇的还原反应。首先,我们将两种不同构型的3-(4-甲氧基苯基)-2-氟-2-烯丙醇在相同条件下分别实施面包酵母还原反应,反应进行48小时后,(Z)-异构体可以基本上完全转化为饱和醇,而(E)-异构体没有明显的反应。为了验证具有不同构型的底物的反应活性差异,我们还考证了4-甲基-2-氟-2-戊烯醇(E：Z=1：9)的面包酵母还原反应。(Z)-异构体反应48小时后基本上完全转化为饱和醇,产物的ee值为91%,而(E)-异构体基本上不被还原。上述结果表明,碳碳双键的构型对2-氟烯丙醇类化合物还原反应的影响是至关重要的。此外,面包酵母还原一系列(Z)-3-烷基-2-氟-2-丙烯醇的反应结果表明,随着烷基链的逐渐增长,还原反应的转化率不断降低。2-氟-6-氯-2-己烯醇和2-氟-2-辛烯醇反应48小时后,转化率均高达99%,并分别以91%和92%对映选择性得到相应饱和醇；当烷基为n-C11H23时,2-氟-2-十四烯醇已经不能被面包酵母还原。更多还原

【Abstract】 Fluoroalcohols are a kind of alcohols contaning fluorine atoms. Because of their unique property, fluoroalcohols as potential intermediates have received much attention in recent years. However, the methods reported for preparing fluorinated primary alcohols with one fluorine atom, especially for introducing a fluorine-containing stereocenter are still few. Therefore, it is necessary to develop new synthetic approaches to chiral primary alcohols with a fluorine-containing stereocenter. In this dissertation, we focous our attention on the study of asymmetric bioreduction of 2-fluoroallyl alcohols mediated by baker’s yeast. By this reaction, chiral fluoroalcohols with high enantioselectivity are obtained.In order to understand the bioreduction mechanism of substituted allyl alcohols, reduction of 2-alkyl-3-arylallyl alcohols mediated by baker’s yeast has been studied in chapter 2. Firstly, the reaction conditions of bioreduction involving pH value, reaction time, concentration of the substrate and the amount of baker’s yeast, have been optimized. Next, the effects of the substituents at both 2-position and 3-position of allyl acohols were investigated. The results showed that with the increase of the size of the substituents at 2-position of allyl acohols, the reaction rate decreased sharply. An obvious increase of the reaction rate has been observed when a phenyl group was replaced by a furyl group at 3-position of allyl alcohols, indicating that the reaction was more favorable with the increase of electron density on C=C bond.Bioreduction of 2-fluorosubstituted cinnamyl alcohols has been studied in chapter 3. As the atomic radius of fluorine is near to that of hydrogen and less effect on electron density on C=C bond,2-fluorocinnamyl alcohol was almost completely converted into saturated alcohol with 81% ee within 48 h, whereas the conversion of 2-bromocinnamyl alcohol was only 5% due to the large size and electron-withdrawing property of bromine. The electronic property of substituents on benzene ring could also affect the bioreduction of 2-fluorosubstituted cinnamyl alcohols. The decrease in electron density on benzene ring 2-fluoro-3-(4-fluorophenyl)-2-propen-1-ol were reduced into their corresponding saturated alcohols with 92% ee and 82% ee within 48 h, respectively, but only 27% of 2-fluoro-3-(4-chlorophenyl)-2-propen-1-ol was converted. In addition, all of the saturated primary alcohols formed from the bioreduction of 2-fluorosubstituted cinnamyl alcohols mediated by baker’s yeast were assigned to be (S)-configuration by analysis of rotation degree and NMR spectra, which is consistent with the stereoselectivity reported previously.In order to broaden the substrate spectrum, the configuration effect of C=C bond and bioreduction of a series of (Z)-3-alkyl-2-fluoro-2-propen-l-ols mediated by baker’s yeast have been studied. Firstly, the bioreduction of (Z)-and (E)-2-fluoro-3-(4-methoxyphenyl)-2-propen-1-ol were performed respectively. (Z)-isomer could be almost completely converted into saturated alcohols within 48h, whereas (E)-isomer couldn’t be reduced by baker’s yeast even the reaction time was prolonged to one week. In order to confirm this remarkable difference in reactivity between (E)-and (Z)-isomers, 2-fluoro-4-methyl-2-penten-1-ol (E:Z=1:9) was also tested. The same difference in reactivity was observed. Only (Z)-isomer could be readily reduced into (S)-2-fluoro-4-methyl-pentan-1-ol with 91% ee after 48 h, and (E)-isomer was totally remained in the reaction mixture. As a result, the configuration of the substrate played a crucial role in the reduction of 2-fluoroallyl alcohols mediated by baker’s yeast. In addition, the results showed that the reaction rate of (Z)-3-alkyl-2-fluoro-2-propen-l-ols decreased sharply with the increase of the alkyl chain length.6-chloro-2-fluoro-2-hexen-1-ol and 2-fluoro-2-octen-1-ol were consumed completely after bioreduction of baker’s yeast within 48 h, and corresponding saturated alcohols were formed with 91%ee and 92% ee respectively. With the alkyl chain length increasing (R=n-C11H23),2-fluoro-2-tetradecen-1-ol was hardly reduced.更多还原