Aromatic Sulfonation. 67.1 Sulfonation of the 1,6-Methano[10]annulene System. Evidence for Ipso Attack with the 2,7-Dimethyl Derivative

Sulfonation of 1,6-methano[ 10]annulene (1) with 0.9 equiv of SO3 in dioxane yields exclusively the 2-sulfonic acid, and with 4 equiv of SO3 only the 2,7-disulfonic acid. The primary kinetic isotope effect for the monosulfonation of 1 was determined to be KH/KD=3.8 ± 0.3. Sulfonation of 2-methyl-l yielded the 5-sulfonic acid. The reaction of 2,7-dimethyl-1 with SO3 in dioxane resulted in peri (65%) and ipso (35%) substitution, with formation of 2,7-dimethyl-l-5-sulfonic acid and 2-methyl-1-7-sulfonic acid, respectively.