Electrochemical oxidative ring opening of 1-methylcyclobutanol

Regioselective Electrochemical Cyclobutanol Ring Expansion to 1‐Tetralones

“… [17–22] The relief of ring strain (strain energy of 26.3 kcal mol −1 ) [23] and the formation of a strong carbonyl bond (179 kcal mol −1 vs 92 kcal mol −1 for C−O bonds) [23] as thermodynamic driving forces enabled the cyclobutanol ring to be established as a versatile precursor to a range of value‐added cores with functional handles and increased molecular complexity [24–27] . For example, in 1996 Nikishin and co‐workers reported the manganese(III)‐mediated electrooxidative ring‐opening to linear ketones [28] . In the same publication they showed that γ‐chlorinated linear butanones were formed as the major product when a chloride salt was added to the electrochemical manganese(III)‐catalyzed cyclobutanol ring‐opening reaction; [28] this work was repeated by Morrill in 2019 [21] .…”

“…For example, in 1996 Nikishin and co‐workers reported the manganese(III)‐mediated electrooxidative ring‐opening to linear ketones [28] . In the same publication they showed that γ‐chlorinated linear butanones were formed as the major product when a chloride salt was added to the electrochemical manganese(III)‐catalyzed cyclobutanol ring‐opening reaction; [28] this work was repeated by Morrill in 2019 [21] . The groups of Zhang and Kim, on the other hand, were particularly productive in the area of tandem functionalization/semi‐pinacol rearrangements and pioneered the electrochemical synthesis of a variety of β‐functionalized cyclopentanones from vinyl‐substituted cyclobutanols [17–20,22] .…”

“…To commence our studies, we drew inspiration from the electrochemical cyclobutanol ring‐opening first reported by Nikishin [28] . Their group showed that through the heterogenous electrochemical formation and regeneration of manganese(III)‐catalysts, alkoxy radicals can be generated from hydroxyl groups through a homogenous single electron transfer ( indirect electrolysis ).…”

“…This alkoxy radical would easily undergo a β‐scission process and lead to the formation of a new carbonyl and carbon‐centred radical. The newly generated radical can then be trapped to furnish diversified γ‐functionalized butanones [28] . We hypothesized that in the absence of an external radical scavenger, these conditions might be amenable to induce intramolecular ring closure.…”

“…We hypothesized that in the absence of an external radical scavenger, these conditions might be amenable to induce intramolecular ring closure. To this end, we treated cyclobutanol 1 a with Mn(OTf) 2 , at a current density of 10 mA.cm −2 , using carbon electrodes and lithium perchlorate/acetonitrile as the supporting electrolyte/solvent system (Table 1, entry 1) [28,39,40] . To our delight, the starting material was completely consumed within three hours (10 F.mol −1 ) and the desired 1‐tetralone 2 a was formed in 32 % yield.…”