Ammonia-driven chirality inversion and enhancement in enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylate mediated by diguanidino-γ-cyclodextrin.

In the supramolecular photocyclodimerization of 2-anthracenecarboxylate mediated by 6(A),6(D)-diguanidino-γ-cyclodextrin (CD), the chiral sense and enantiomeric excess of the photoproduct were dynamic functions of temperature and cosolvent to afford the (M)-anti head-to-head cyclodimer in 64% ee in aqueous methanol at -70 °C but the antipodal (P)-isomer in 86% ee in aqueous ammonia at -85 °C, while the corresponding diamino-γ-CD host did not show such unusual photochirogenic behaviors. The ee landscape was very steep against the temperature and sign-inverted against the ammonia content to reveal the opposite temperature dependence at low and high ammonia contents, for which an altered solvent structure and/or guanidinium-carboxylate interaction mode would be responsible.