Oxidative coupling of alkynes mediated by nitroxyl radicals under Sonogashira conditions and Pd-free catalytic approach to stable radicals of 3-imidazoline family with triple bonds

In the presence of Pd catalyst, 3-imidazoline nitroxyl radicals promote oxidative coupling (dimerization) of terminal alkynes even in the absence of Cu(II) additives. On the other hand, the Pd-free CuI-PPh3-K2CO3-DMF catalytic system leads to the efficient cross-coupling of 1-hydroxy-4-[2-(p-iodophenyl)vinyl]-2,2,5,5-tetramethyl-3-imidazoline-3-oxide with terminal aryl- and hetarylacetylenes with the formation of 4-[2-(aryl/hetarylethynyl)phenyl)vinyl]-2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyls in 70-75% yields.