Manipulating [2?+?2] photodimerization of 1,4-dihydropyridines within ?-cyclodextrin

Irradiation of 1,4-dihydropyridines (DHPs) in the presence of γ-cyclodextrin (γ-CD) performs an efficient formation of the cage-dimer under a medium-pressure mercury lamp. The cage-dimer yields for DHPs complexed within γ-CD may achieve approximately 80%, far higher than those in the non-complexed state. It is postulated that the available cavity volume in γ-CD is responsible for the observed selectivity. The formation of 1:2 host-guest inclusion complex plays an important role in this reaction, and manipulates DHPs to perform [2 + 2] photodimerization as expected. In order to investigate the inclusion process, the spectral characteristics were investigated and the theoretical study was performed using density functional theory (DFT).