Copper-catalyzed Carbon-Nitrogen/Carbon-Selenium Bonds Formation: Synthesis of 2-(Organochalcogenyl)-Indolizines

The copper catalyzed cyclization of propargyl pyridines with diorganyl dichalcogenides was applied to the synthesis of 2-(organochalcogenyl)-indolizines. Systematic study of the cyclization system revealed that the mutual action between copper(I) iodide and diorganyl dichalcogenides is essential for the formation of indolizines in good yields avoiding the formation of hydrogenated indolizine. The standard reaction conditions were compatible with many functional groups in the substrates, such as methyl, chlorine, fluorine, methoxyl and trifluoromethyl. This protocol was efficient to diorganyl diselenides and ditellurides but ineffective to diorganyl disulfides. In addition, the obtained 2-(organochalcogenyl)-indolizines were readily transformed to more complex products by reaction with boronic acids using palladium-catalyzed cross-coupling conditions