Direct Electrochemical α-Deuteration of Secondary Benzylic Alcohols in Flow

A direct electrochemical method for the α-deuteration of secondary benzylic alcohols is described. Sequential paired electrolysis in a flow system couples anodic alcohol oxidation with cathodic reductive deuteration on graphite electrodes. Deuterium oxide serves as the sole deuterium source, with lithium tetrafluoroborate as the supporting electrolyte. No further molecular catalyst or soluble redox mediator is needed. The deuterated model alcohol is isolated in 72% yield with 90% deuterium incorporation, and selected substituted benzhydrols undergo similarly high labeling.Cyclic voltammetry and reaction-progress studies support an alcoholketone redox sequence. Competitive oxidation experiments reveal preferential depletion of the protiated isotopologue, consistent with isotope-dependent discrimination that contribute to deuterium enrichment.