On the relative reactivity of the C C double bond and the [10] annulene moiety versus SO3

Sulfonation of 11‐methylene‐1,6‐methano[10]annulene (6a) with 1, 3, 4 or 6 equivalents of the dioxane‐SO3 complex in dioxane results in the formation of the 2‐sulfonic acid (6b) as the exclusive 1H NMR detectable product, whereas 1,6‐methano‐[10]annulene (5a) with 3 equiv. of this sulfonating agent already yields the 2,7‐disulfonic acid. The lower reactivity of the peripheral ring of 6a compared with that of 5a is explained in terms of a higher coplanarity of the annulene ring of 6a.