The electrochemical Wittig‐Horner reaction; evidence of a stepwise cleavage of a four‐membered ring Wittig intermediate

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Abstract
Electro‐reduction of diethyl(trichloromethyl)phosphonate in the presence of aldehydes or ketones replaces the oxygen atom of the carbonyl group by a dichloromethylene group. The yield of 1,1‐dichloroethene product decreases substantially if the carbonyl compound carries strongly acidic hydrogen. In several cases the conversion of the four‐membered ring Wittig intermediate into its corresponding carbanion by heterolytic PC bond cleavage is observed. The intermediate carbanion is sufficiently stable to be intercepted by proton abstraction. These observations suggest that, at least with our substrates, the decomposition of the Wittig four‐membered ring intermediate occurs along a two‐step path way.