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

Abstract

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 Ph3PR+ 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 Sc3+ as mediator in the TPPO electroreduction been uncovered by density functional theory calculations.

Perspective on intermetallics towards efficient electrocatalytic water-splitting

“…Alternatively, the same electrochemical technology with intermetallics can be applied in non-aqueous solvents to drive the other essential transformations such as regeneration of the triphenylphosphine from triphenylphosphine oxide as well as a one-pot Wittig olefination reaction that presently best driven by noble-metal catalysts. 238 Furthermore, the scope of the intermetallics can easily be extended electrochemical carbon dioxide (CO 2 ) reduction, a promising reaction to mitigate CO 2 emissions, where presently transition metals (in particularly Cu) have been used predominantly to yield high-end multicarbon products. Notably, the intermetallics can also be of special interest for the kinetically sluggish oxygen reduction reaction (ORR), an important cathodic reaction of fuel cell which is presently mediated by the metals, alloys, and carbons, etc.…”

“…Alternatively, the same electrochemical technology with intermetallics can be applied in non-aqueous solvents to drive the other essential transformations such as regeneration of the triphenylphosphine from triphenylphosphine oxide as well as a one-pot Wittig olefination reaction that presently best driven by noble-metal catalysts. 238 …”

Electroreduction: A Sustainable and Less Energy‐Intensive Approach Compared to Chemical Reduction for Phosphine Oxide Recycling to Phosphine

“…Sevov et al used AlCl 3 and tetralkylammonium salt as additives in which AlCl 3 makes a coordinate bond with oxygen of the "P=O" bond followed by activation of TPPO. [93] Furthermore, an isolable ionic salt could also be prepared from a reaction mixture of TPPO and AlCl 3 . [94] Very similar to Elias' observation, a change in redox peak feature of TPPO was reported by Sevov and confirmed that a 0.33 equivalent of AlCl3 is sufficient to activate the TPPO presumably due to a 1 : 3 stoichiometry of AlCl 3 : TPPO in solution state (Figure 5d).…”

Organic Electrochemistry: Expanding the Scope of Paired Reactions

“…[42] We hoped that the increased reactivity of the Ph 3 As = O might make its reduction compatible with an anodic cyclization in the presence of the required methanol solvent and thereby provide information on the reduction potential needed for such a process. This alternative for Ph 3 P=O was intriguing because Geary and co-workers have demonstrated that Wittig reactions can be conducted with the use of Ph 3 As in place of the Ph 3 P. [43,44] The reduction of Ph 3 As=O was initially paired with the oxidation of veratryl alcohol [Scheme 10, Eq. (a)].…”