Electroreductive Cyclization. Ketones and Aldehydes Tethered to α,β-Unsaturated Esters (Nitriles). Fundamental Investigations

Article abstract of DOI:10.1021/jo00245a029

The intramolecular electrochemically initiated cyclization of a variety of α,β-unsaturated esters and one nitrile, each of which is tethered to an aldehyde or a ketone, has been investigated.Good yields (70-79percent) of mono- and bicyclic products, resulting from closure between the β-carbon of the α,β-unsaturated unit and the aldehyde or ketone carbonyl carbon, were obtained.Cyclic voltammetry was used to determine that the α,β-unsaturated unit corresponded to the electrophore.In all but one instance, cyclization favored formation of the product wherein the hydroxy and (methoxycarbonyl)methyl units were trans to one another.The stereoselectivity was studied as a function of temperature, nature of the proton donor, proton availability, and percent conversion (i.e., as a function of time).Attempts to use the reaction to synthesize the marine natural product ambliol A were unsuccessful.A mechanistic scheme in which a reversible cyclization of the initially formed radical anion is followed by an irreversible proton transfer is suggested to account for the experimental observations.