Electrochemistry of Diphenylcyclopropenone in Aprotic Solvents: Electrochemical Synthesis of Oligomers and Electrochemically Driven Decarbonylation Reaction

Abstract

We have shown that electrochemistry of Diphenylcyclopropenone (1) in aprotic solvents presents some interesting and peculiar aspects.¹ For instance, (a) the voltammetric curves clearly show that the irreversible reduction of (1) in DMF at a G.C. electrode is followed by a polymerization-dimerization process, by which a new substance is formed; this species shows reversible behaviour at more positive potentials (Figure 2); (b) a preparative electrolysis in the same solvent system and at a moderate concentration of (1) originates monomeric decarbonylation and fragmentation-rearrangement products, as for example Diphenylacetylene (tolan) (2), Benzylphenylketone (3), Benzophenone (4) (all isolated and identified), together with an oligomeric-derived mixture of (5) and (6) (GC, EI.MS).² Now, we report that the preparative electrochemistry of (1), in repeated experiments,(DMF-TEAP 0.1 M and R.V.C. electrode, concentration of (1) 10⁻² M), produces the new substances (7), (8) and (9), all isolated and identified by ¹H-NMR, ¹³C-NMR (decoupled and DEPT) (Figure 1), and FABMS. To this purpose, work-up was carried out in two stages: firstly, the oligomeric fractions were separated from a polymeric mixture, which was not further investigated. The oligomeric mixture was then processed, thus obtaining products (7)–(9). The simplest way to reconcile the above mentioned results is as follows: anion radical of A=(1), A^·-once formed at the electrode, may decarbonylate to (2), rearrange, or dimerize-polymerize. Three different types of polymers may be anticipated, and correspondingly, all the types of the above mentioned oligomeric products follow.