Chemistry of thienopyridines. XII. Selective formation of N‐oxides, sulfoxides, and sulfones in some tricyclic systems

Direct conversion of [1]benzothieno[3,2‐b]pyridine (IVa), thieno[3,2‐b:4,5‐b']dipyridine (Va), and thieno[2,3‐b:4,5‐b']dipyridine (VIa) into their sulfoxides was effected by means of an equimolar quantity of iodobenzene dichloride in aqueous acetonitrile. Treatment of IVa‐VIa with excess chlorine gas in carbon tetrachloride and then with water gave the corresponding sulfones, IVc‐VIc. Hydrogen peroxide in glacial acetic acid converted Va and VIa into di‐N‐oxides, thieno[3,2‐b]pyridine into its N‐oxide, and sulfone VIc into an N‐oxide sulfone (X). Spectral and chemical means of distinguishing amongst the oxide functions are noted, and rationalizations for selectivity in the oxidations are discussed.