Department of Chemistry , University of Pittsburgh , Pittsburgh , Pennsylvania 15208 , United States.
J Am Chem Soc. 2019 Aug 7;141(31):12355-12361. doi: 10.1021/jacs.9b05547. Epub 2019 Jul 23.
Reactions of readily available alkenyl triflates with N-heterocyclic carbene (NHC)-boranes in the presence of diisopropyl ethyl amine provided about three dozen stable α-NHC-boryl ketones. Isolated yields were typically 40-56% for B-unsubstituted NHC-boranes (NHC-BH), and somewhat lower for NHC-boranes with B-substituents (NHC-BHR). 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 α-NHC-boryl ketone, SO, 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.
readily available alkenyl triflates 与 N-heterocyclic carbene (NHC)-boranes 在二异丙基乙胺的存在下反应，提供了约三十多种稳定的 α-NHC-硼基酮。未取代的 NHC-硼烷 (NHC-BH) 的分离产率通常为 40-56%，而带有 B 取代基的 NHC-硼烷 (NHC-BHR) 的产率略低。所需的烯基三氟甲磺酸酯可以分别制备，也可以从酮或炔烃原位制备。实验证据支持涉及以下步骤的自由基链机制：(1) NHC-硼基自由基加成到烯基三氟甲磺酸酯，(2) 断裂生成 α-NHC-硼基酮、SO 和三氟甲基自由基，以及 (3) 三氟甲基自由基从起始的 NHC-硼烷中抽取氢，同时生成 NHC-硼基自由基和三氟甲烷。反应 1 和 3 都是新的，显然非常快。
