A photochemical [2 + 2 + 1] radical annulation of 2-vinyloxy arylalkynes with bromomalonates has been developed. This protocol affords a transition-metal-free, oxidant-free and base-free approach to cyclopenta[b]benzofurans under mild conditions. This tandem reaction involves sequential radical addition, 5-exo-dig cyclization, 1,5-H shift, 5-endo-trig annulation, radical coupling, and elimination processes. Significantly, the photoinduced C–Br bond homolysis of bromomalonates involves an energy transfer, and the solvent DMF acts as an acid-binding reagent.

中文翻译：

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2-乙烯基氧基芳基炔与溴代丙二酸酯通过能量转移进行光化学[2 + 2 + 1]环化

已开发出 2-乙烯基氧基芳基炔与溴代丙二酸酯的光化学 [2 + 2 + 1] 自由基环化反应。该方案提供了一种在温和条件下无过渡金属、无氧化剂和无碱的环戊[ b ]苯并呋喃方法。该串联反应涉及连续的自由基加成、5- exo-dig环化、1,5-H 移位、5- end-trig成环、自由基偶联和消除过程。值得注意的是，光诱导的溴代丙二酸酯的 C-Br 键均裂涉及能量转移，而溶剂 DMF 充当酸结合剂。