Methyl Radical Initiated Kharasch and Related Reactions,Advanced Synthesis & Catalysis

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Methyl Radical Initiated Kharasch and Related Reactions
Advanced Synthesis & Catalysis ( IF 4.4 ) Pub Date : 2020-10-25 , DOI: 10.1002/adsc.202001000
Nicholas D. C. Tappin ₁ , Philippe Renaud ₁

Affiliation

An improved procedure to run halogen atom and related chalcogen group transfer radical additions is reported. The procedure relies on the thermal decomposition of di‐tert‐butylhyponitrite (DTBHN), a safer alternative to the explosive diacetyl peroxide, to produce highly reactive methyl radicals that can initiate the chain process. This mode of initiation generates byproducts that are either gaseous (N₂) or volatile (acetone and methyl halide) thereby facilitating greatly product purification by either flash column chromatography or distillation. In addition, remarkably simple and mild reaction conditions (refluxing EtOAc during 30 minutes under normal atmosphere) and a low excess of the radical precursor reagent (2 equivalents) make this protocol particularly attractive for preparative synthetic applications. This initiation procedure has been demonstrated with a broad scope since it works efficiently to add a range of electrophilic radicals generated from iodides, bromides, selenides and xanthates over a range of unactivated terminal alkenes. A diverse set of radical trap substrates exemplifies a broad functional group tolerance. Finally, di‐tert‐butyl peroxyoxalate (DTBPO) is also demonstrated as alternative source of tert‐butoxyl radicals to initiate these reactions under identical conditions which gives gaseous by‐products (CO₂).

中文翻译：

甲基自由基引发的Kharasch及其相关反应

据报道，一种改进的方法可以运行卤原子和相关的硫族基转移自由基。该程序依赖于二丁基亚硫酸氢盐（DTBHN）的热分解，后者是爆炸性二乙酰过氧化物的安全替代品，可产生可引发链过程的高反应性甲基。这种引发方式产生的副产物要么是气态的（N ₂）或挥发性（丙酮和甲基卤化物），从而极大地促进了通过快速柱色谱或蒸馏的产物纯化。另外，非常简单和温和的反应条件（在常压下于30分钟内回流EtOAc）和少量过量的自由基前体试剂（2当量）使该方案对制备合成应用特别有吸引力。该引发程序已经得到了广泛的应用，因为它可以有效地将一系列由碘化物，溴化物，硒化物和黄药生成的亲电子基团添加到一系列未活化的末端烯烃上。多种自由基捕获底物集体现了广泛的官能团耐受性。最后，二叔过氧草酸丁酯（DTBPO）也被证明是叔丁氧基自由基的替代来源，可在相同条件下引发这些反应，产生气态副产物（CO ₂）。

更新日期：2020-10-25

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