Cu(I)-Catalyzed Intramolecular Tandem Cyclization of N-Indole-Tethered Cyclopropenes: Synthesis of Functionalized Hydrogenated Diazabenzo[a]cyclopenta[cd]azulene Derivatives

A Cu(I)-catalyzed [3 + 2] intramolecular cycloaddition reaction of N-indole-tethered cyclopropenes is presented in this paper. This reaction starts from the formation of π-allyl cationic intermediate or its resonance-stabilized metal carbenoid intermediate upon activation of cyclopropene with Cu(I) catalyst and a Friedel–Crafts-type cyclization to give functionalized hydrogenated diazabenzo[a]cyclopenta[cd]azulenes in good to excellent yields along with moderate to good dr values. The asymmetric variant of this cycloaddition reaction can be realized, giving the desired products with moderate ee values.