Cu/Rh-Carbene-Directed Highly Diastereoselective Dimerization of Cyclopropenes

Carbene dimerization typically proceeds through head-to-head coupling to form planar olefins. Herein we report a carbene dimerization of cyclopropenes under copper or rhodium catalysis that proceeds through sequential C–H insertion and [2 + 1] cycloaddition to furnish cyclopropa-fused indanes with excellent diastereoselectivities. The reaction features broad substrate scope, gram-scale synthesis, and versatile product transformations. Mechanistic studies and DFT calculations reveal that π–π stacking interactions govern the high diastereoselectivity.