Palladium-catalyzed and ligand-controlled divergent cycloadditions of vinylidenecyclopropane-diesters with para-quinone methides enabled by zwitterionic π-propargyl palladium species

Abstract

A palladium-catalyzed divergent synthesis of spiro-cyclohexadienones with a five- or a six-membered ring by a cycloaddition reaction of vinylidenecyclopropane-diesters (VDCP-diesters) with p-quinone methides (p-QMs) was disclosed. This protocol features a switchable process between [3 + 2] and [4 + 2] cycloadditions tuned by subtle choice of the phosphine ligand. The substrate scopes have been investigated and the reaction mechanism has been clarified by mechanistic studies; and DFT calculations also revealed that the coordination modes of the ligands with the substrates and the bite angle of the ligands play critical roles in the product regioselectivity.