Facile Synthesis of α-N-Heterocyclic Carbene-Boryl Ketones from N-Heterocyclic Carbene-Boranes and Alkenyl Triflates
Facile Synthesis of α-N-Heterocyclic Carbene-Boryl Ketones from N-Heterocyclic Carbene-Boranes and Alkenyl Triflates
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DOI：
10.1021/jacs.9b05547
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发表时间：
2019-08-07
影响因子：
15
通讯作者：
Curran, Dennis P.
中科院分区：
文献类型：
--
作者：
Dai, Wen;Geib, Steven J.;Curran, Dennis P.
容易获得的烯基三氟甲磺酸酯与N-杂环卡宾（NHC）-硼烷在二异丙基乙胺存在下的反应提供了约36种稳定的α-NHC-硼基酮。B-未取代的NHC-硼烷（NHC-BH 3）的分离产率通常为40-56%，而具有B-取代基的NHC-硼烷（NHC-BH 2 R）的分离产率稍低。所需的烯基三氟甲磺酸酯可以单独制备或由酮或炔原位制备。实验证据支持自由基链机理，其涉及以下：（1）将NHC-硼基自由基加成到三氟甲磺酸烯基上，（2）断裂以得到α-NHC-硼基酮、SO 2和三氟甲基自由基，以及（3）通过三氟甲基自由基从起始NHC-硼烷夺取氢以使NHC-硼基自由基沿着三氟甲烷返回。反应1和3都是新的，而且显然相当快。
Reactions of readily available alkenyl triflates with N-heterocyclic carbene (NHC)-boranes in the presence of diisopropyl ethyl amine provided about three dozen stable alpha-NHC-boryl ketones. Isolated yields were typically 40-56% for B-unsubstituted NHC-boranes (NHC-BH3), and somewhat lower for NHC-boranes with B-substituents (NHC-BH2R). The requisite alkenyl triflates can be made separately or prepared in situ from either ketones or alkynes. The experimental evidence supports a radical chain mechanism that involves the following: (1) addition of an NHC-boryl radical to the alkenyl triflate, (2) fragmentation to give the alpha-NHC-boryl ketone, SO2, and trifluoromethyl radical, and (3) hydrogen abstraction by trifluoromethyl radical from the starting NHC-borane to return the NHC-boryl radical along with trifluoromethane. Reactions 1 and 3 are both new and evidently rather fast.