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