【作者】 张江华；

【导师】 赵德丰； 高欣钦；

【作者基本信息】 大连理工大学 ， 应用化学， 2010， 博士

【摘要】 硼氢化物复合体系是实现官能团转化反应的重要还原体系之一。目前,硼氢化钠、硼氢化钾与金属氯化物、质子酸、卤素等添加剂构成的各种硼氢化物复合还原体系已见文献报道,但上述体系在进行底物还原反应时存在化学选择性不好(如：AlCl3/NaBH4)、还原效果差(如：MgCl2/KBH4、H2SO4/NaBH4)等缺点。本论文实现了HfCl4/KBH4、HfCl4/NaBH4两种新型硼氢化物复合体系对羧酸及其衍生物、亚砜类化合物、二硫化物、环氧化物等诸多底物的还原反应,并对以上缺点加以克服。首先,对HfCl4/硼氢化物体系下羧酸及其衍生物的还原反应进行了研究。考察了不同溶剂、反应温度、底物/HfCl4/硼氢化物的摩尔比对该还原反应的影响,分别优化了HfCl4/KBH4体系、HfCl4/NaBH4体系还原羧酸及其衍生物的反应条件。上述二体系在优化的反应条件下,实现了对脂肪族、芳香族羧酸及其衍生物的高收率还原反应(收率最高可达98%),且该还原方法具有反应条件温和(反应温度为40℃)、有化学选择性(底物分子中的卤素、硝基等官能团有兼容性)等优点。其次,研究了HfCl4/硼氢化物体系下亚砜类化合物的脱氧还原反应。分别优化了HfCl4/KBH4、HfCl4/NaBH4体系还原亚砜类化合物的反应条件,实现了二体系对二烷基、二芳基、烷基芳基等亚砜类化合物的高收率还原反应(收率最高可达99%),尤其对难以被其它体系还原的二苯基(HfCl4/KBH4体系,收率93%；HfCl4/NaBH4体系,收率98%)、二苄基亚砜(HfCl4/KBH4体系,收率97%；HfCl4/NaBH4体系,收率99%)可以进行高收率的脱氧还原反应,且在反应过程中底物分子中的卤素、硝基、甲氧基等官能团不受该还原体系的影响。在上述研究的同时,探讨了微波辅助作用下HfO2/NaBH4、nano-HfO2/NaBH4、HfCl4/HfO2/NaBH4、HfCl4/nano-HfO2/NaBH4等体系对二苄基亚砜的无溶剂环境友好脱氧还原反应,但发现其中的nano-HfO2/NaBH4体系得到的产物收率相对较高,仅为37%。此外,对HfCl4/硼氢化物体系下其它底物的还原反应及竞争性还原反应也进行了相应研究。结果表明,在HfCl4/KBH4体系下,过氧酸m-CPBA能够被还原为3-氯苄醇(收率为73%),二硫化物能被快速还原为相应的硫醇或硫酚产物；在HfCl4/NaBH4体系下,二苯甲酮在165℃下能被还原为二苯甲醇与二苯甲烷的混合产物(摩尔比为73：27)。但HfCl4/硼氢化物体系对环丁砜、二苯基砜没有还原作用,且不能将对甲苯磺酸、对甲苯磺酰氯还原为相应的苯硫酚产物。值得关注的是,在对HfCl4/KBH4体系下环氧化物的开环反应进行研究时,发现该体系在室温下15 min内能将环氧苯乙烷还原为2-苯乙醇(收率为78%),且粗产中未检测到副产物1-苯乙醇的生成；当环氧苯乙烷分别与羧酸、羧酸酯、腈、酰胺等底物共存于反应体系时,该体系还能于室温下对环氧苯乙烷进行化学选择性、空间选择性还原。与催化加氢方法及其它化学还原方法相比,该法具有操作简单、反应条件温和、反应时间短、收率高、化学选择性好等优点。更多还原

【Abstract】 Borohydride complex system is one of the most important reducing systems of functional-group transformations. In recent years, various combinations of borohydrides (NaBH4, KBH4) and certain additives, such as metal halides, protonic acids, and halogens have been reported. However, most of the reported reducing systems suffer from various drawbacks, like lower chemoselectivity (e. g., AlCl3/NaBH4), weaker reducing ability (e. g., MgCl2/KBH4、H2SO4/NaBH4), etc.. In this dissertation, efficient and chemoselective reductions of some derivatives, like carboxylic acids and their derivatives, sulfoxides, disulfides, epoxides and so on by new borohydride complex systems (HfCl4/kBH4 and HfCl4/NaBH4 systems) are reported.Reduction of carboxylic acids and their derivatives by HfCl4/borohydride systems is firstly studied in this dissertation. Considering the effect of solvent, reaction temperature, and molar ratio of substrate/HfCl4/borohydride on the reaction, the experimental conditions of HfCl4/KBH4 and HfCl4/NaBH4 systems are optimized respectively. Then under optimum conditions, aliphatic, aromatic carboxylic acids and their derivatives can be reduced to the corresponding alcohols in excellent yields (up to 98%) at 40℃without any change to halogen-, and nitro-groups in substrates.HfCl4/KBH4 and HfCl4/NaBH4 systems are also attempted to reduce sulfoxides. The experimental conditions are optimized firstly. Then under optimized mild conditions, HfCl4/KBH4 and HfCl4/NaBH4 systems are found to be facile, efficient, and chemoselective reagents for the deoxygenation of dialkyl, diaryl, and aryl alkyl sulfoxides in excellent yields (up to 99%), especially for deoxygenation of diphenyl sulfoxide in yields of 93% and 98% respectively and dibenzyl sulfoxide in yields of 97% and 99%, which are difficult to reduce by other reagents. Besides, functional groups, such as halogen-, nitro-, and methoxy-groups are tolerated in the reduction process. Meanwhile, the microwave-assisted reduction of dibenzyl sulfoxide under solventless and environmental conditions by HfO2/NaBH4, nano-HfO2/NaBH4, HfCl4/nano-HfO2/NaBH4 or HfCl4/Hf02/NaBH4 system has been developed, but it is found that only the deoxygenation by nano-HfO2/NaBH4 system reaches a relatively high yield of 37%.Furthermore, the reduction and competitive reduction of some other substrates by HfCl4/borohydride systems are investigated. And the results are shown as follows. By using HfCl4/KBH4 system, m-CPBA is reduced to 73% of 3-chlorobenzyl alcohol, and disulfides can be rapidly reduced to the corresponding thiols or thiophenols. By using HfCl4/NaBH4 system, benzophenone is reduced to a mixture of diphenylmethanol and diphenylmethane (molar ratio= 73:27) at 165℃. However, the attempted reduction of sulfolane and diphenyl sulfone results in only the recovery of starting materials.p-Toluenesulfonic acid and p-toluenesulfonyl chloride can not be reduced to the corresponding thiophenols. Meanwhile, in research after the reductive ring-opening reaction of epoxides by HfCl4/KBH4 system, it is found that styrene oxide is regioselectively reduced to 78% of 2-phenylethanol without the formation of 1-phenylethanol. Besides, competitive reduction of styrene oxide in the presence of carboxylic acid, carboxylic ester, nitrile and amide is achieved at room temperature by HfCl4/KBH4 system, which features chemo-and regio-selective reduction of epoxide. Compared with catalystic hydrogenation and other chemical reduction methods, it is more facile, efficient, and chemoselective.更多还原