Regio- and stereoselective [2+2] photocycloaddition in Ba2+ templated supramolecular dimers of styryl-derivatized aza-heterocycles

The regio- and stereoselective [2+2] photocycloaddition of 15-crown-5-containing styrylheterocycles resulting in formation of only one cyclobutane isomer out of eleven possible is described. It was shown that the cycloaddition takes place solely in the case of the supramolecular preorganization of the reactive molecules provided by both π–π stacking interaction of the heterocyclic fragments and sandwich-type coordination of the crown ether residues by the barium cation. The results point out the importance of the supramolecular approach for the synthesis of cyclobutane derivatives with desired structure and conformation. © 2016 Elsevier Ltd