Radical anions containing the dioxidated 1,2,5-thiadiazole heterocycle

Radical anions of 3,4-aryl disubstituted 1,2,5-thiadiazole 1,1-dioxide were obtained by chemical and electrochemical reduction of their substrates, and characterized by ESR spectroscopy and cyclic voltammetry. The radical anion of the phenanthro[9,10-c]-1,2,5-thiadiazole 1,1-dioxide was found to be very stable in an aprotic solvent solution and did not react readily when water was added to the aprotic solvent, or the solution was saturated with oxygen gas. The radical formation chemical reaction competed with nucleophilic addition to the C=N bond of the thiadiazoles. A possible reaction mechanism, and a common reaction intermediate, supported by density functional theory calculations, is presented for the most stable radical. Copyright (C) 2009 John Wiley & Sons, Ltd.