many bidentate box-based lewis acid-catalyzed reactions are based on copper(ii) catalysts with substrates that are suitable for two-point binding. the stereochemical outcome is consistent with a twisted square planar intermediate that was proposed based on related crystal structures. the substituent at the oxazoline's 4-position blocks one enantiotopic face of the substrate, leading to enantioselectivity. this is demonstrated in the following aldol-type reaction, but is applicable to a wide variety of reactions such as mannich-type reactions, ene reaction, michael addition, nazarov cyclization, and hetero-diels-alder reaction.