Ferricyanide oxidation of 1-substituted pentaphenylpyridinium salts. A novel route to 1-substituted 2,3,4,5-tetraphenylpyrroles

Oxidation of 1-substituted 2,3,4,5,6-pentaphenylpyridinium salts Ia-Ij by potassium ferricyanide in an alkaline medium yields the corresponding 1-substituted 2,3,4,5-tetraphenylpyrroles in 68 to 76% yields. The selectivity of the reaction is discussed.