Topochemical, Single‐Crystal‐to‐Single‐Crystal [2+2] Photocycloadditions Driven by Chalcogen‐Bonding Interactions

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 cyclobutane formation through single-crystal-to-single-crystal [2+2] photodimerizations. chelating 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 SeO2 malononitrile in 75–90 % yield. very short intramolecular Se⋅⋅⋅Se distance 1–3 (3.22–3.24 Å), a consequence strong ChB interaction, expands 3.52–3.54 Å chalcogen-bonded adducts with bpen, (<4 Å) well adapted bpen reactive position toward photochemical dimerization.