Umpolung reactivity of indole through gold catalysis.
Umpolung reactivity of indole through gold catalysis.
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DOI：
10.1002/anie.201103014
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发表时间：
2011-08-29
影响因子：
16.6
通讯作者：
Zhang, Liming
中科院分区：
文献类型：
--
作者：
Lu, Biao;Luo, Yingdong;Liu, Lianzhu;Ye, Longwu;Wang, Yanzhao;Zhang, Liming
The indole 3-position is highly electron-rich and typically functions as the primary nucleophilic site to react with a large array of electrophiles, leading to various functionalized indoles.[1] The reversal of this prime reactivity, ie, making the indole 3-position electrophilic, would be of significant synthetic utility and provide a complementary strategy to access derivatives [2] otherwise difficult to prepare conventionally. This reactivity umpolung [3] of indole has, however, only been realized in limited cases.[4]For the past few years we have engaged in extensive studies of gold-catalyzed intra-[5] and intermolecular [6] alkyne oxidations using oxygen-delivering oxidants,[7] where reactive αoxo gold carbene intermediates are presumably generated [8] and responsible for the diverse reaction outcomes. Lately we extended this strategy to the use of nitrene precursors as oxidants, providing access to reactive α-imino gold carbenes (Scheme 1A);[9] however, the chemistry has so far been limited to ynamides,[10] which are activated alkynes. In our effort to expand the scope of this type of gold-catalyzed nitrene transfer,[11] we decided to use an azido group as a nitrene precursor, which was inspired by previous studies of gold-[12] and platinum-catalyzed [13] pyrrole synthesis. We reasoned that closely and rigidly positioned CC triple bonds in ortho-azidoarylalkynes might facilitate an intramolecular nitrene transfer from the azido group to the CC triple bond. Importantly, the thus-formed gold carbene B would serve as an electrophilic indole equivalent, as depicted in its resonance form C, therefore realizing reactivity umpolung of the indole 3-position (Scheme 1B).[14]
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