Formal Pericyclic‐Coupled Electron Transfer: I. Stepwise Formal Diels‐Alder Cycloaddition Enabled by Addition‐Coupled Electron Transfer.

The formal Diels‐Alder (D−A) reaction of alkenes with 1,2‐diimine and related substrates is designed and studied by density functional theory (DFT), multi‐reference and quasi‐classical trajectory calculations in the presence of a benzoquinone‐based organic oxidant. The reaction is found to occur through an Addition‐Coupled Electron Transfer (ACET) with one electron transferred to the oxidant in one elementary step, affording a carbon‐radical, followed by an intramolecular radical addition. The overall barrier is significantly reduced as compared to the traditional concerted D−A reaction. The reaction with two new bond formation events in one elementary step coupled with electron transfer (concerted Pericyclic‐Coupled Electron Transfer, cPeriCET) was not found. This work reveals that coupling to electron transfer might be a tool to achieve cycloaddition reactions with unactivated substrates. [ABSTRACT FROM AUTHOR]