A Divergent Synthesis of Spiroindenes via Ligand-Controlled [3+2]/[4+2] Cycloadditions of Zwitterionic π-Propargyl Palladium Species with Benzofulvenes

Abstract

A divergent synthesis of spiroindenes through a palladium catalyzed cycloaddition between zwitterionic π-propargyl palladium species and benzofulvenes in moderate to good yields has been disclosed along with good functional group compatibility and a broad substrate universality. This protocol features a highly regioselective switchable process between [3+2] and [4+2] cycloadditions controlled by phosphine ligands with different bite angles. The reaction mechanism has been clarified by mechanistic studies and DFT calculations, rendering that the coordination modes of the ligands with the substrates and the bite angle of the ligands play critical roles in the product regioselectivity.