Sulfonation of trans‐10b,10c‐dimethyl‐10b,10c‐dihydropyrene and its 2,7‐di‐tert‐butyl derivative with sulfur trioxide

Abstract

AbstractThe sulfodeprotonation of trans‐10b,10c‐dimethyl‐10b,10c‐dihydropyrene (1) with sulfur trioxide has been studied in dioxane as solvent, as well as in dichloromethane, using 4.0–5.0 equivalents of dioxane relative to the amount of SO3 as reactivity moderator. Reaction of 1 with 0.6 mol‐equiv. of SO3 in dioxane at 22°C yields initially only the 2‐ and 4‐sulfonic acid in a 84/16 ratio. Using 3.0‐6.0 mol‐equiv. of SO3 in dichloromethane with the temperature increasing from −78 up to 22°C the initially very rapid formation of the 1‐, 2‐ and 4‐sulfonic acid (formed in a ratio of 11/82/7) is followed by a much slower conversion into a mixture of 1,7‐, 2,4‐, 2,5‐ and 2,7‐disulfonic acid. These four acids are subsequently converted even more slowly into a mixture of the 1,4,7‐, 2,4,7‐ and 2,5,9‐trisulfonic acids to yield in part the 1,4,7,9‐, 2,4,7,9‐ and 2,4,7,10‐tetrasulfonic acids. trans‐2,7‐Di‐tert‐butyl‐10b, 10c‐dimethyl‐10b, 10c‐dihydropyrene (2) with 0.8–2.0 equiv. of SO3 in dioxane as solvent gives the 4‐sulfonic acid which is slowly converted into a 16/84 mixture of the 4,9‐ and 4,10‐disulfonic acids.The observed distributions of sulfonic acid isomers are discussed in terms of the directing effects of the “ideal” ‐ almost planar ‐ [14] annulene and the sulfo and/or tert‐butyl substituent(s) already present.