Copper-Catalyzed (2+1) Annulation of Acetophenones with Maleimides: Direct Synthesis of Cyclopropanes.

A practical copper-catalyzed direct oxidative cyclopropanation of electron-deficient alkenes with acetophenone derivatives is reported. The dehydrogenative annulation involves a double C-H bond functionalization at the α-position of the ketone using di-tert-butyl peroxide as oxidant. The broad scope of the reaction and excellent functional-group tolerance is demonstrated for the stereoselective synthesis of fused cyclopropanes. The developed transformation revealed an unprecedented reactivity for copper-catalyzed processes.