Dibenzothiophenes electrophilic substitution

These relative reactivities correlate reasonably well with the observed electrophilic substitution reactions of dibenzothiophene, the 1-position being realistically portrayed by this series of experiments. 

Carbazole 332, dibenzofuran 333 (Z=0), and dibenzothiophene 333 (Z=S) behave as diphenylamine, diphenyl ether, and diphenyl sulfide, respectively, in their substitution reactions and thus electrophilic substitution occurs at the positions para to the heterocyclic atom, as exemplified for ... 

N.B. Competition between the sulfonium formation and that of sulfoxide can be clearly exemplified with dibenzothiophene, where two different types of bases are used in situ (extraction of protons). With lutidine, sulfoxide is obtained probably from the residual water contained in the lithium perchlorate. On the contrary, insoluble bases (like inorganic carbonates) appear to strongly favor a mild electrophilic substitution. 

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