Facile access to -substituted piperazin-2-ones and mianserin derivative enabled by chemoselective carbene insertion and cyclization cascade.

The chemoselective N-H insertion of unsymmetrical diamines into carbene is a longstanding challenge. A simple copper-catalyzed strategy for synthesizing -substituted piperazinones is described, employing easily accessible diazo compounds and 1,2-diamines. The reaction proceeded chemo-selective carbene insertion at the comparatively less nucleophilic amine, followed by instantaneous cyclization. The protocol was further extended to access NH-free piperazinone, and the synthesis of a Mianserin derivative.