Hantzsch Ester-Mediated Photochemical Transformations in the Ketone Series: Remote C(sp³)–H Arylation and Cyclopentene Synthesis through Strain Release

A metal-free Hantzsch ester-mediated synthesis of cyclopentenylketones as well as γ-hetarylketones starting from ketocyclopropanes under eco-friendly conditions was developed. The versatility of the developed conditions is shown by reacting ketocyclopropanes in both a formal [3 + 2] cycloaddition with terminal alkynes (further investigated using theoretical calculations) and a radical C–C-coupling with cyanopyridines. The newly developed methodologies were later on utilized as a downstream reaction for photogenerated cyclopropanes combining UV and visible light photochemistry. Following this procedure, a UV-driven Norrish–Yang-type reaction induces the ring strain of the intermediates, which serves as activation energy for the subsequent ring transformation.本研究开发了一种无金属介导、以汉斯酯（Hantzsch ester）为试剂的合成策略，可在环保友好条件下以环丙基酮（ketocyclopropanes）为起始原料合成环戊烯基酮（cyclopentenylketones）与γ-杂芳基酮（γ-hetarylketones）。通过使环丙基酮分别与末端炔烃（terminal alkynes）发生形式[3+2]环加成反应（后续通过理论计算对该反应开展了深入探究）、与氰基吡啶类化合物（cyanopyridines）发生自由基C-C偶联（radical C–C-coupling）反应，验证了所开发方法的底物普适性。随后，该新开发的合成方法被用作结合紫外光与可见光光化学（UV and visible light photochemistry）的光生环丙烷（photogenerated cyclopropanes）的下游反应。按照该实验流程，紫外光驱动的诺里什-杨型反应（Norrish–Yang-type reaction）可诱导中间体的环张力（ring strain），以此作为后续环结构转化的活化能（activation energy）。