Photoinduced Formal Cross-[3+3] Cycloaddition of Vinyldiazo Reagents with Acceptor-Only Diazoalkanes

In this study, we devised an innovative approach for the synthesis of pyrazine derivatives through a photoinduced formal cross-[3+3] cycloaddition between vinyldiazo reagents and acceptor-only diazoalkanes. This method leverages the differential reactivity of two distinct diazo compounds: vinyldiazo reagents, which upon visible light irradiation form key cyclopropane intermediates, and acceptor-only diazoalkanes, which function as 1,3-dipoles to capture the photogenerated reactive species. The reactions proceed exclusively under visible light, yielding 1,4-dihydropyridazines with a broad substrate scope and compatibility with various functional groups. Importantly, the synthesized 1,4-dihydropyridazines can be readily converted to other valuable products. The mechanism, elucidated through UV-vis absorption studies, deuterium labeling experiments, control experiments, and in situ NMR spectroscopy, provides a clear understanding of the observed reactivity.