Electron-acceptor-sensitized splitting of cyclobutane-type thymine dimers

Abstract

Chloranil- and 9,10-dicyanoanthracene-sensitized reactions of 1,3-dimethylthymine dimers were investigated. Cis—syn and trans—syn isomers underwent cyclobutane ring opening to yield the parent monomer. Anti-type dimers did not react under these conditions. The effect of solvent polarity on the quantum yield and the quenching of the reaction in the presence of 1,2,4-trimethoxybenzene support the idea that the cycloreversion proceeds via electron transfer from the dimers to the excited sensitizer. The same reaction, although much less efficient, was observed for cis—syn intramolecular adduct derived from 3,3′-dimethyl-1,1′-trimethylene-bisthymine. The reason for this inefficiency is discussed. In the case of all reactive cyclobutanes, the corresponding thymine monomers were accompanied by additional products containing incorporated sensitizer molecules.