Photoredox Catalytic Cascade Radical Addition to Construct 1,4-Diketone-Functionalized Quinoxalin-2(1H)-one Derivatives

The biological importance of quinoxalin-2(1H)-ones has inspired increasing pursuit for the development of efficient and expedient synthetic methods to access these entities. Among them, C3-H functionalization of quinoxalin-2(1H)-ones has been a sought-after strategy in recent years, especially using photocatalysis platform to trigger radical intermediates. Besides the direct addition of photocatalysis-yielding radicals to 3-position of quinoxalin-2(1H)-ones, a handful of threecomponent cascade reactions have been described, wherein olefins were used to preferentially accept radicals to generate new radical intermediates to experience the second addition process. Given the robust ability of cascade strategy to enrich the varieties of quinoxalin-2(1H)-ones, the exploration of new protocols remains a highly attractive task. Herein, we report photoredox catalytic reactions of quinoxalin-2(1H)-ones with 2-bromo-1-arylethan-1-ones as the partners, leading to a series of valuable 1,4-diketone-functionalized quinoxalin-2(1H)-one derivatives with satisfactory results. This is an unprecedented cascade reaction strategy, involving radical addition to quinoxalin-2(1H)-ones and the resultant intermediates to accept a second addition of radicals generated from bromide substrates or to experience S(N)2 reaction with bromides.

Automated summary

The biological importance of quinoxalin-2(1H)-ones has driven the development of efficient synthetic methods. In recent years, C3-H functionalization has become a popular strategy, especially using photocatalysis to generate radical intermediates. This study reports a cascade reaction strategy involving radical addition to quinoxalin-2(1H)-ones and subsequent reactions to generate a series of valuable quinoxalin-2(1H)-one derivatives. The reaction partners used in this study are 2-bromo-1-arylethan-1-ones.