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=OSO2CF3(OTf)), affording the corresponding [Ph3POR](+)X(-)salts which undergo efficient electroreduction to TPP in the presence of a substoichiometric amount of the Sc(OTf)(3)Lewis acid on a Ag-electrode. Subsequent alkylation of TPP affords Ph(3)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(3+)as mediator in the TPPO electroreduction been uncovered by density functional theory calculations.