Colouring Matters Derived from Pyrroles. Part I I .

Dimerization of 3-substituted 2-oxindoles has been developed under a mild electrochemical condition, avoiding toxic chemical oxidants and metal by-products. This methodology forms a C­(sp3)–C­(sp3) bond at the pseudobenzylic position of two partners of 2-oxindoles with a broad substrate scope. These dimeric structural motifs are important building blocks for the total synthesis of pyrroloindoline alkaloids. Furthermore, this work demonstrates in-depth mechanistic insights employing electrochemistry, which suggests a stepwise one proton transfer (PT) and two electron transfer (ET) processes. Most significantly, reaction rate acceleration has been demonstrated by exploiting the base-assisted proton-coupled electron transfer (PCET) pathway. Hence, this work brings a new dimension in the field of electro-organic synthesis with the help of nature’s favorite kinetic route, i.e., PCET, to lower the kinetic barrier.

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Electrochemical strategy has been the powerful approach for the synthesis of valuable intermediates, in particular heterocyclic motifs. It has proven to be an environmentally benign, highly effective and versatile platform...