A Systems Approach to a One-Pot Electrochemical Wittig Olefination Avoiding the Use of Chemical Reductant or Sacrificial Electrode.

An unprecedented one-pot fully electrochemically driven Wittig olefination reaction system without employing a chemical reductant or sacrificial electrode material to regenerate triphenylphosphine (TPP) from triphenylphosphine oxide (TPPO) and base-free in situ formation of Wittig ylides, is reported. Starting from TPPO, the initial step of the phosphoryl P=O bond activation proceeds through alkylation with RX (R=Me, Et; X=OSO CF (OTf)), affording the corresponding [Ph POR] X salts which undergo efficient electroreduction to TPP in the presence of a substoichiometric amount of the Sc(OTf) Lewis acid on a Ag-electrode. Subsequent alkylation of TPP affords Ph PR which enables a facile and efficient electrochemical in situ formation of the corresponding Wittig ylide under base-free condition and their direct use for the olefination of various carbonyl compounds. The mechanism and, in particular, the intriguing role of Sc as mediator in the TPPO electroreduction been uncovered by density functional theory calculations.