Topochemical, Single‐Crystal‐to‐Single‐Crystal [2+2] Photocycloadditions Driven by Chalcogen‐Bonding Interactions
Jan Alfuth, Olivier Jeannin, Marc Fourmigué
Abstract
Abstract The face‐to‐face association of ( E )‐1,2‐di(4‐pyridyl)ethylene ( bpen ) molecules into rectangular motifs stabilized for the first time by chalcogen bonding (ChB) interactions is shown to provide photoreactive systems leading to cyclobutane formation through single‐crystal‐to‐single‐crystal [2+2] photodimerizations. The chelating chalcogen bond donors are based on original aromatic, ortho ‐substituted bis(selenocyanato)benzene derivatives 1 – 3 , prepared from ortho ‐diboronic acid bis(pinacol) ester precursors and SeO 2 and malononitrile in 75–90 % yield. The very short intramolecular Se⋅⋅⋅Se distance in 1 – 3 (3.22–3.24 Å), a consequence of a strong intramolecular ChB interaction, expands to 3.52–3.54 Å in the chalcogen‐bonded adducts with bpen , a distance (<4 Å) well adapted to the face‐to‐face association of the bpen molecules into the reactive position toward photochemical dimerization.