Origin of site-selectivity of hydrogen atom transfer in carbohydrate C-H alkylations via photoredox catalysis

The mechanism and origin of site-selectivity in carbohydrate C-H alkylations via photoredox catalysis were investigated using DFT calculations and the approach of energy decomposition analysis. The results reveal that diphenylborinic acid can promote the reactivity by lowering the barrier of the lactonization process. The effect of diphenylborinic acid on the site-selectivity of HAT is mostly due to the enhanced charge transfer from the sugar C-H sigma orbital to the nitrogen SOMO of the quinuclidine radical cation. An effective binary linear regression model, including C-H sigma orbital energy and C-H BDE, has been proposed for predicting the site-selectivity of the sugar HAT process.