The structure of thiophene sesquioxide: Syn, endo‐3a,4,7,7a‐tetrahydro‐4,7‐epithiobenzo[b] thiophene 1,1,8‐trioxide

Thiophene sesquioxide is shown to be syn, endo‐3a,4,7,7a‐tetrahydro‐4,7‐epithiobenzo[b]‐thiophene 1,1,8‐trioxide (I) by 1 H and 13 C nmr evidence. Assignment of the 13 C spectrum was facilitated by a cross‐ring long‐range 13 C‐1 H coupling. The mass spectrum of I is dominated by an unusual break‐down to give benzene radical cation.