Electron Donor–Acceptor Complex Enabled Radical Cyclization of α-Diazodifluoroethyl Sulfonium Salt with Unactivated Alkynes

Alkoxy Diazomethylation of Alkenes by Photoredox-Catalyzed Oxidative Radical-Polar Crossover

“…In 2018, our group reported a new photocatalytic synthesis of valuable aryl diazoacetates based on a diazomethylation of aryl C–H bonds with cyclic and pseudocyclic diazomethyl-substituted hypervalent iodine reagents (Figure B). , Key to this work was the photocatalytic generation of electrophilic diazomethyl radicals [N 2 C­(·)CO 2 R], which are reactive equivalents of doublet carbynes. Later on, other groups showed that such radicals, generated with our hypervalent iodine reagents or sulfonium analogues as well as terminal diazo compounds, were prone to undergo [3 + 2] cyclizations with hydrazones, acyl radicals, alkynes, quinoxalinones or styrenes providing access to five-membered heterocycles as well as ring expansions of indenes . In the latter cases, the diazo functionality was not preserved as such and participated in the cyclization or even dinitrogen was eliminated during the process.…”