Transition-metal-catalyzed olefin cross-metathesis plays an important role in the construction of various carbogenic skeletons by allowing the exchange of substituents between different olefins via an activated key intermediate consisting of a four-membered ring coordinated to a transition metal. [1] Alternatively, electrochemical reactions have proven to be a viable method in triggering reactions between different olefins by reversing the polarity of alkenes [2] and initiating radical anion- [3] (or cation- [4] ) based reactions.[5] Electrochemically activated olefin cyclodimerization, for example, can effectively lead to the intermolecular formation of fourmembered rings.[6] Moreover, we reported an electrocatalytic intermolecular formal [2 + 2] cross-coupling of electron-rich olefins (Scheme 1).[7] The anodic oxidation of enol ethers [8] that bear a methoxyphenyl group can be used to trigger an intermolecular formal [2 + 2] cycloaddition with varied alkenes. In this case, the intermolecular olefin coupling was assisted by a unique lithium perchlorate/nitromethane electrolyte solution [9] and the methoxyphenyl group of the substrates served as an intramolecular electron donor [10] to form the cyclobutane ring. Herein, we describe novel electrochemical olefin cross-metatheses between anodically activated enol ethers and aliphatic alkenes.Initially, the electrolytic intermolecular reaction between 4-methoxybut-3-enylbenzene (1) and hex-1-ene (2) was investigated. The anodic oxidation of enol ether 1 involved a carbon felt anode, a constant potential of 1.43 V (vs. Ag/ AgCl), a carbon felt counter electrode, and a lithium perchlorate/nitromethane electrolyte solution (1.0 m) in an undivided cell under argon. Remarkably, the anodic activation of enol ether 1 in the presence of 2 resulted in the formation of but-3-enylbenzene (3) in 78 % yield (Scheme 2).In our experiments, the reaction was deemed complete after the passage of approximately 1.0 F mole À1 of electricity. Under different electrolytic conditions, the desired product was obtained in trace or in unacceptable yields (Table 1). In the absence of electrolysis, a mixture of 1 and 2 in lithium perchlorate/nitromethane electrolyte solution at ambient temperature did not react, even after more than 10 h. Furthermore, the reaction was responsive to a stepwise application of the electricity. Because the amount of the product for each stage remained essentially unchanged during the intervals of electrolysis, an external switch of the electrolysis allows the regulation of the reaction process.The electrochemical enol ether/olefin cross-metathesis can also be extended to the combination of simple alkyl enol ethers and alkenes. For example, anodic oxidation of 1-methoxy-tridec-1-ene (4) in the presence of 2 afforded the desired tridec-1-ene (5) in 76 % yield (Scheme 3).To gain insight into the reaction mechanism, the anodic activation of enol ether 1 was carried out with deuteriumScheme 1. Anodic intermolecular formal [2 + 2] cross-coupling of olefins.Scheme 2....
