Calcium-catalyzed Friedel–Crafts addition of 1-methylindole to activated cyclopropanes

The synthesis of γ-indolyl malonates was achieved through the addition of indoles to activated cyclopropanes. These Friedel–Crafts reactions were catalyzed by calcium bis(trifluoromethanesulfonimide), Ca(NTf2)2. The addition proceeded with complete regioselectivity and in good to excellent yields. Optimization of the reaction conditions and investigation into the scope of the reaction with regard to substitution on cyclopropane are reported.