Recent Advances in Stereoselective [2+2+2] Cycloadditions

Abstract The [2+2+2] cycloaddition reaction is considered one of the most efficient methods for the rapid and straightforward preparation of complex polycyclic (and heterocyclic) compounds in a highly selective and atom‐economical fashion. Over the last half‐century, remarkable advances in terms of chemo‐ and regioselectivities have been realized, endowing this reaction with attractive features as a key step in the synthesis of various biologically active molecules and materials. The development of stereoselective methodologies is more recent. In this field, asymmetric transition‐metal catalysis has emerged as the most convenient tool with which to perform these [2+2+2] cycloadditions in their enantio‐ and diastereoselective variants. All the catalytic systems that have been developed so far are based on very close association of a transition metal (Co, Ni, Ir, Rh, ...) with a chiral ligand. The success of these reactions is then related to the reaction pattern involved (inter‐ and intramolecular), implying an efficient substrate/active species interaction. Thus, judicious design both of chiral ligands and of unsaturated substrates is necessary. In light of these aspects, numerous stereoselective cycloadditions have been reported; these allow the construction in one‐step fashion of central, axial, planar, and helical chiralities. This review details the recent advances in this area, with specific attention to catalysts and reaction scope.