Aromatic Sulfonation, 130 . – Relative Intramolecular Reactivity of the Insulated π Double Bond and the 14π Annulene Perimeter toward Sulfur Trioxide in the Sulfonation of Isopyrenes

The sulfonation of isopyrene ( 1 ) and its 5‐methyl‐ and 5,10‐dimethyl derivative 2 and 3 with SO 3 in both dichloromethane and nitromethane as solvent has been studied. Reaction of 1 and 2 leads to sulfodehydrogenation in which SO 3 reacts as a monodentate electrophile, the initial products being 1 ‐5‐sulfonic acid ( 1 ‐5‐S) and 2 ‐10‐S, respectively. In the presence of a sufficiently large amount of SO 3 1 ‐5‐S is subsequently converted into 1 ‐5,10‐S 2 . With 3 , using 2.0 molequiv, of the sulfonating reagent in dichloromethane, the SO 3 adds as a bidentate electrophile to the “central C=C bond” with formation of 7,14‐dimethyl‐1,6:8,13‐ethanediylidene‐[14]annulene‐15,16‐sultone ( 5 ) and the corresponding pyrosultone 6 . Upon subsequent hydrolysis and neutralization with aqueous KOH the eventually obtained product is potasium 16‐hydroxy‐7,14‐dimethyl‐1,6:8,13‐ethanediylidene‐[14]annulene‐15‐sulfonate ( 4 ).