Intramolecular [2 + 2] Photocycloaddition of Benzene Derivatives─Chiral Induction in Cyclodextrin Inclusion Complexes.

The cyclodextrin (CD) complexes of several butenyloxybenzonitriles were synthesized and irradiated as aqueous suspensions. An enantioselective intramolecular [2 + 2] or ortho photocycloaddition in such inclusion complexes is described. α-Cyclodextrin and β-cyclodextrin induce chirality in the opposite direction. At the reaction temperature (<7 °C), the enantiomeric excess (ee) is significantly increased (34% for α-CD, -10% for β-CD). The product yield in the cyclodextrin complex (35%) was close to that one of the racemic reaction in solution (42%). A topological analysis describes C2-symmetric chiral induction in a C6-symmetric host structure (α-Cyclodextrin). In a computational study, the energies of the inclusion complex were calculated for different conformations of compound 3a.