Reaction optimization and mechanism in maleimide [5 + 2] photocycloaddition: a dual approach using tunable UV lasers and time-dependent DFT.

An in-depth study of the intramolecular [5 + 2] photocycloaddition of maleimides using tunable UV lasers has demonstrated that the peak in quantum yield and rate both occur at wavelengths some 50 nm red shifted from the maxima observed in the UV spectra. A detailed explanation for these findings using time-dependent DFT calculations is presented, and the implications for a previously adopted mechanism are discussed.