Electrocatalytic intermolecular olefin cross-coupling by anodically induced formal [2+2] cycloaddition between enol ethers and alkenes.

Electrochemical reactions have proven to be valuable means for reversing the polarity of alkenes and triggering radical anionor radical cation-based cyclizing reactions. Anodic olefin coupling initiated by oxidation of electronrich olefins can provide powerful tools for achieving intramolecular cyclization reactions and building new ring systems. In this case, several combinations of olefins can be introduced in the intramolecular cyclizing system, securing diverse functional groups in the newly cyclized skeletons. Electrocatalytic intermolecular cyclodimerization of olefins has been achieved for fourmembered-ring formation. On the other hand, it has unfortunately been difficult to achieve electrolytic intermolecular selective cross-coupling of two different olefins to provide the [2+2] cycloadduct. This was disappointing because the electrochemical method might allow for the selective polarity inversion of electron-rich olefins and open the door for the construction of fourmembered rings by new combinations of olefins even in neutral conditions. This gave us the incentive to try to determine whether such an electrochemical approach might provide a unique pathway to their selective intermolecular olefin cross-coupling to construct [2+2] cycloadducts between the in situ-generated electrondeficient olefins and non-activated ones under the regulation of oxidation potentials and intraand intermolecular electron transfers. We report herein our initial efforts to develop the novel electrocatalytic intermolecular formal [2+2] cross-coupling of electronrich olefins. Initially, the electrolytic cycloaddition between enol ethers 1-3 and allyltrimethylsilane 4 was studied (Fig. 1).