A Novel Synthesis of Alkylboranes Using Addition Reaction of Alkyl Radicals

利用烷基自由基加成反应合成烷基硼烷的新方法

• 批准号: 06650973
• 负责人: HOSHI Masayuki
• 金额: $ 0.19万
• 依托单位: Kitami Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1995
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06650973/
• 关键词: alkylborane; alkyl radical; tributyltin hydride; alkyl halide; alkene; hydroboration; phenylethyne; 3-bromo-1-propene

A novel synthesis of alkylboranes, which can not be obtained regioselectively by hydroboration of alkenes, was investigated in this research. It is well known that the addition reaction of an alkyl radical to an electron deficient alkene, mediated with tributyltin hydride, proceeds regioselectively to carry out carbon-carbon bond formation. Accordingly, the addition reaction was applied to synthesize alkylboranes.2-Phenylethenylborane, prepared by monohydroboration of phenylethyne, was regarded as an electron deficient alkene, and it was subjected to the tributyltin hydride mediated coupling of alkyl halides with electron deficient alkenes. The reaction of some alkyl halides was examined in the presence of a small amount of AIBN under reflux in benzene or under irradiation by a mercury lamp at room temperature. It was found that the reaction proceeded under both reaction conditions to give the corresponding 1-phenyl-2-alkylboranes where the alkyl radical was introduced regioselectively into the alpha-alkenyl carbon atom. The resulting alkylboranes were unable to be prepared regioselectively by usual hydroboration. The reaction of alkyl halides with 2-phenylethenylboronic acid under reflux gave good results, because the reaction using 2-phenylethenylboronic acid did not result in steric hindrance between alkyl radical and boryl group.Next 3-bromo-1-propylborane, prepared by hydroboration of 3-bromo-1-propene, was regarded as an alkyl halide, and the reaction with electron deficient alkenes was examined in a similar manner. 3-Bromo-1-propylborane was reduced to propylborane with tributyltin hydride via radical process, whereas it was difficult to undergo the reaction with electron deficient alkenes. Accordingly, it is needed to examine the reaction using other haloalkenes.

本研究研究了一种新的烷基硼烷合成方法，该方法不能通过烯烃硼氢化反应来区域选择性地获得。众所周知，由氢化三丁基锡介导的烷基自由基与缺电子烯烃的加成反应可区域选择性地进行以形成碳-碳键。因此，应用加成反应合成烷基硼烷。通过苯乙炔单硼氢化反应制备的2-苯基乙烯基硼烷被视为缺电子烯烃，并通过三丁基氢化锡介导的卤代烷与缺电子烯烃进行偶联。在少量 AIBN 存在下，在苯中回流或室温汞灯照射下，研究了一些烷基卤化物的反应。发现反应在两种反应条件下进行，得到相应的1-苯基-2-烷基硼烷，其中烷基被区域选择性地引入到α-烯基碳原子中。所得烷基硼烷不能通过常规硼氢化反应区域选择性地制备。卤代烷与2-苯基乙烯基硼酸在回流下的反应得到了良好的结果，因为使用2-苯基乙烯基硼酸的反应不会在烷基和硼基之间产生空间位阻。接下来将3-溴-1-丙烯硼氢化制备的3-溴-1-丙基硼烷视为卤代烷，并与缺电子烯烃反应 以类似的方式进行了检查。 3-溴-1-丙基硼烷用氢化三丁基锡通过自由基过程还原为丙基硼烷，而与缺电子烯烃很难发生反应。因此，需要检查使用其他卤代烯烃的反应。