Photochemical Reaction Of Pyrimindine Derivatives With Substituted Benzophenones And Photoisomerization Of Cinnamic Acid Derivatives

The Paternò-Büchi (P-B) reaction is a photochemical [2+2] cycloaddition of carbonyl compounds with alkenes, giving substituted oxetanes. When the two triplet-exited 1,4-diradicals formed in the P-B reaction possess silimar stablitity, the regioselectivity will be determined by other factor such as the polarity of solvent, temperature and substituent. We investigated the P-B reaction of 1,3-dimethylthymine (DMT) with 4-methoxybenzophenone (MBP) in acetonitrile-water binary solvent with kinds of proportion. Notable solvent effects on the regioselectivity and the photochemical efficiency were observed. Solvent effect of regioselectivity can be explained by the frontier moclecular orbital (FMO) theory; and solvent effect of the photochemical efficiency may be responsible for the strongly solvent-dependent properties of the triplet-excited MBP. In this work, we also investigated two subsidiary reactions in the P-B reaction of 1,3,6-trimethyluracil/ 1,3,6-trimethylthymine (TMU/TMT) with 4,4'-disubstited benzophones (BPs), and gived their reaction mechanisms. One is the second-order photo reaction of the hh oxetanes formed in the P-B reaction; and another is a competitive radical coupling reaction with the P-B reaction.Olefins including cinnamate derivatives can perform cis-tran isomerization through directly irradiation or photosensitized by triplet-state photosensitizer. We investigated photoisomerization of the cinnamic acid derivatives resulting from the intramolecular T-T energy transfer from the covalently linked triplet benzophenone unit. On the basis of phosphorescence quenching experiments, we drawn a conclusion that: T–T energy transfer to the E isomer is more efficient than to the Z isomer. Trans-o-hydroxycinnamate occurs cis-trans isomerization after absorbing a photo. The hydroxy of Cis-o-hydroxycinnamate attacks the adjacent carbonyl and a fluorescent coumarin was obtained after a lactonization course. Taking advantage of this reaction, we prepaired a photolabile protecting group for alcohol which is water soluble and can be used as internal fluoresce reporting for the releasing exrtent of caged alcohol.