Unique solvent effect of water in radical cyclization reaction.

The radical cyclization reaction in the aqueous environment by Yorimitsu et al. is revisited using the RISM-SCF-cSED method, a hybrid of quantum chemistry and statistical mechanics theory for molecular liquids. The difference between the barrier height of the forward reaction from the intermediate E -rot, the cyclization step, and that of the backward reaction is crucial to the reaction yield. Considering the effect of hydrogen bonding through the RISM theory, we found that the barrier height for the forward reaction is lower, especially in water. In other words, considering microscopic solvation effects clearly shows the difference between water and DMSO solvents, explaining the remarkable acceleration of the reaction in the aqueous environment. [Display omitted] • The solvent effect on the radical cyclization reaction is analyzed theoretically. • Water solvent promotes the cyclization reaction by lowering its transition state. • Hydrogen bond around C O oxygen atom plays a crucial role on solvent effect of water. • The change in solvation structure along with the C C bond formation is also revealed. [ABSTRACT FROM AUTHOR]