"Snapshots" of Intramolecular Electron Transfer in Redox Tag-Guided [2 + 2] Cycloadditions.

Although single electron transfer (SET) is widely illustrated in formal expressions, it is not rationally supported by computational studies. The present work provided "snapshots" of intramolecular SET in redox tag-guided [2 + 2] cycloadditions, enabled by density functional theory calculations. Significant shifts of spin and positive charge are observed in relation to the carbon-carbon bond formation in the cyclobutyl framework, which is in excellent accordance with a formal expression of the reaction mechanism.