Benzophenone vs. Copper/Benzophenone in Light‐Promoted Atom Transfer Radical Additions (ATRAs): Highly Effective Iodoperfluoroalkylation of Alkenes/Alkynes and Mechanistic Studies,Advanced Synthesis & Catalysis

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Benzophenone vs. Copper/Benzophenone in Light‐Promoted Atom Transfer Radical Additions (ATRAs): Highly Effective Iodoperfluoroalkylation of Alkenes/Alkynes and Mechanistic Studies
Advanced Synthesis & Catalysis ( IF 4.4 ) Pub Date : 2016-08-31 , DOI: 10.1002/adsc.201600501
Redouane Beniazza ₁ , Rachel Atkinson ₁ , Christelle Absalon ₁ , Frédéric Castet ₁ , Sergey A. Denisov ₁ , Nathan D. McClenaghan ₁ , Dominique Lastécouères ₁ , Jean-Marc Vincent ₁

Affiliation

Iodoperfluooralkylation of terminal alkenes and alkynes is effectively photo‐promoted by benzophenone 2 (BP) or the photoreducible copper(II) complex 1. In particular, BP at 1 mol% in methanol upon 365 nm irradiation with a low‐pressure mercury lamp (type TLC=thin layer chromatography, 6 W) results in a fast reaction with excellent reaction yields. Complex 1 and BP 2 exhibited very similar reactivity, suggesting that the reactions involving 1 are likely to be governed by the benzophenone photoactivation processes, rather than copper(I)/(II) redox processes. Mechanistic investigations using transient absorption spectroscopy revealed that a deactivation pathway of the benzophenone triplet (³BP*) is via its reaction with the methanol solvent. We propose that the generated radicals, in particular ^.CH₂OH, play a key role in the initiation step forming R_f^. by reacting with R_fI, R_f^. then entering a radical chain cycle. ¹H NMR studies provided evidence that a substantial amount (∼7% NMR yield) of the hemiacetal CH₃OCH₂OH is formed, i.e., the possible by‐product of the reaction between ^.CH₂OH and R_fI. Finally, DFT calculations indicate that a triplet‐triplet energy transfer (TTET) process from ³BP* to perfluorooctyl iodide (C₈F₁₇I) is unlikely or should be rather slow under the reaction conditions, consistent with the transient absorption studies.

中文翻译：

光促进的原子转移自由基加成（ATRA）中的苯甲酮与铜/苯甲酮：烯烃/炔烃的高效碘全氟烷基化及机理研究

二苯甲酮2（BP）或光还原性铜（II）络合物1有效促进了末端烯烃和炔烃的碘过氟烷基化。尤其是，在低压汞灯（TLC =薄层色谱，6 W）照射365 nm时，甲醇中1摩尔％的BP可以实现快速反应，并具有出色的反应产率。配合物1和BP 2表现出非常相似的反应性，表明涉及1的反应很可能是由二苯甲酮的光活化过程而不是铜（I）/（II）氧化还原过程控制的。使用瞬态吸收光谱的机理研究表明，二苯甲酮三联体的失活途径（³BP *）是通过其与甲醇溶剂的反应来进行的。我们建议特别是生成的部首^。CH ₂ OH在形成R _f的引发步骤中起关键作用^。通过与R _f I，R _f反应^。然后进入一个彻底的连锁循环。¹ H NMR研究提供了证据，表明形成了大量（约7％NMR）半缩醛CH ₃ OCH ₂ OH，即之间可能发生的副产物^。CH ₂ OH和R _˚F I.最后，DFT计算表明，从三线态-三线态能量传递（TTET）工艺与瞬态吸收研究一致，在反应条件下，将³ BP *转化为全氟辛基碘化物（C ₈ F ₁₇ I）的可能性不大，或者应该相当缓慢。

更新日期：2016-08-31

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