Electrochemistry of a spirolactone

The 1,2,6,7-tetraphenyl-4-oxa-spiro[2.4]hepta-1,6-dien-5-one (spirolactone, 1) has been prepared and investigated with reference to its redox properties, using cyclic voltammetry and controlled potential electrolysis in dimethylformamide (DMF) using Et4NClO4 as supporting electrolyte. The most relevant features are the three reduction steps, Ep1=−1.68 V, Ep2=−2.34 V, Ep3=−2.62 V (SCE) which are irreversible on the time scale of the voltammetric experiments used. The first electron/molecule transfer, with no corresponding anodic process, gives rise to an unstable radical anion, which, by rupture of the three-membered ring at the spiro carbon, rearranges to a distonic radical anion. The presence of 5-(1,2-diphenyl-vinyl)-3-(5-hydroxy-1,2,6,7-tetraphenyl-4-oxa-spiro[2.4]hepta-1,6-dien-5-yl)-3,4-diphenyl-3H-furan-2-one (5) (40%) among the isolated products, after controlled potential electrolysis, points to a further attack of the distonic radical anionic species on the starting compound 1. Thus, the dimeric unsymmetric lactone 5 retains the spiro structure in one half of the molecule.