Dramatic effects of the electrolyte cation on the selectivity of electroreductive cycloaddition reactions of bis(enones)

The nature of the electrolyte cation (Li, Na, K, Ag, Mg, Ba) exerts a dramatic effect upon the diastereoselectivity of the intramolecular cyclobutanation reactions of several bis(enones). The formation of cis as against trans cyclobutanes is strongly favored by magnesium ions, presumably via a chelation effect, and becomes exclusive in the case of barium. The latter ion has the additional surprising effect of enhancing the amount of Diels–Alder cycloaddition as opposed to cyclobutanation.