Initiation of radical cyclisation reactions using dimanganese decacarbonyl. A flexible approach to preparing 5-membered rings
Initiation of radical cyclisation reactions using dimanganese decacarbonyl. A flexible approach to preparing 5-membered rings
复制标题
DOI：
10.1039/b000835o
复制
发表时间：
2000-01-01
期刊：
影响因子：
--
通讯作者：
Whittaker, DTE
中科院分区：
文献类型：
--
作者：
Gilbert, BC;Kalz, W;Whittaker, DTE
使用可见光光解十羰基二锰[Mn-2（CO）（10）]产生五羰基锰自由基[Mn-。（CO）（5）]，其与有机卤化物反应形成碳中心自由基。有效的卤素原子提取发生在烯丙基或苄基卤化物或带有弱碳-卤素键的多卤代前体。空间相互作用也很重要，伯卤化物通常与Mn-反应快得多。（CO）（5）比仲或叔卤化物。以碳为中心的基团可以进行有效的二聚化，或者在受体双键存在下，环化形成5元环。末端烯烃的环化导致初级自由基，然后初级自由基可以通过碘或溴原子转移反应，或者在加入丙-2-醇时通过氢原子转移反应。当在克里思存在下进行环化反应时，也可以形成羟胺。这些高产率的环化捕获反应在温和的反应条件下引发，并且卤化锰副产物[XMn（CO）（5）型]可以通过简单的DBU后处理程序容易地与产物分离。
Photolysis of dimanganese decacarbonyl [Mn-2(CO)(10)] using visible light produces the manganese pentacarbonyl radical [Mn-.(CO)(5)] which reacts with organohalides to form carbon-centred radicals. Efficient halogen-atom abstraction occurs with allylic or benzylic halides or polyhalogenated precursors bearing a weak carbon-halogen bond. Steric interactions are also important and primary halides generally react much faster with Mn-.(CO)(5) than secondary or tertiary halides. The carbon-centred radicals can undergo efficient dimerisation or, in the presence of an acceptor double bond, cyclisation to form 5-membered rings. Cyclisation of terminal alkenes leads to primary radicals, which can then react by iodine- or bromine-atom transfer or, on addition of propan-2-ol, hydrogen-atom transfer. Hydroxylamines can also be formed when cyclisation reactions are carried out in the presence of TEMPO. These high-yielding cyclisation-trapping reactions are initiated under mild reaction conditions and the manganese halide by-products [of type XMn(CO)(5)] can be easily separated from products by a simple DBU work-up procedure.