NHC-Boryl Radical Catalysis for Cycloisomerization With C–C Triple Bond Reorganization

Abstract

Our present study unveils a new and efficient Nheterocyclic carbene (NHC)-boryl radical-catalyzed cycloisomerization of N-(2-ethynylaryl)arylamides. This catalytic process is triggered by the addition of an NHC-boryl radical to the alkynyl moiety, followed by a radical cascade comprising of an intramolecular cyclization, successive 1,5-and 1,2-aryl migrations, and the reorganization of a CC triple bond. Eventually, the catalytic cycle is achieved through a radical β-fragmentation reaction, from which the starting NHC-boryl radical is regenerated, and a structurally important quinolinone framework is assembled. A 13 C-labeling experiment was carried out to verify the CC triple bond reorganization, and the proposed catalytic pathway was supported further by density functional theory calculations. Our identification of NHC-boryl radical as a catalyst, as well as its mode of operation via radical addition/elimination mechanism, would stimulate the advancement of design of radical catalysis and the discovery of novel enantioselective radical-catalyzed processes.

New Radical Borylation Pathways for Organoboron Synthesis Enabled by Photoredox Catalysis

“…Reactions involving boryl radicals as key intermediates have been found to proceed via distinct mechanisms, enabling pertinent molecular transformations . In particular, N ‐heterocyclic carbene (NHC)‐boryl radicals have emerged as a class of powerful reactive species to enable various significant syntheses and catalysis . In this context, Curran, Taniguchi, and Walton, as well as our research group, have independently developed a series of radical borylation reactions with alkenes and alkynes for the synthesis of organoboron molecules (Scheme a).…”

Recent Advances in the Construction of Fluorinated Organoboron Compounds

“… 60 , 61 Especially, NHC-boryl radicals have been widely investigated and were proven to be a class of powerful reactive species that allows various significant synthesis 62 and catalysis. 63 Originating from the robustness of the C–F bond and the lack of an efficient catalytic system, direct C–F bond borylation of polyfluoroarenes that generate fluorinated organoboron compounds remains challenging. However, some examples on the construction of fluorinated organoboron compounds via radical-promoted monodefluoroborylation have been reported in recent years ( Scheme 7 ).…”

Lewis-Base Boryl Radicals Enabled Borylation, Radical Catalysis and Reduction Reactions

“…2019 年, 肖文精和陈加荣课题 组 [42] 利用烯烃和烯丙基砜为原料, 氮自由基作为催化 剂, 实现了一例烯烃的分子间双官能团化反应, 开辟了 氮自由基在催化领域的新应用. 2019 年, 我们课题组 [43] 利用氮杂环卡宾-硼自由基作为催化剂, 实现了一例有 机分子骨架的重排反应( Scheme…”