Thieno thiophenes bromination, chlorination

Since bromination and chlorination result in a greater variety of di-substituted products of thieno[2,3-Zi]thiophene 1 than of thieno[3,2-6]-thiophene 2, the conclusion has been drawn that a halogen in position 2 in thienothiophene 1 deactivates position S to a lesser extent than in thienothiophene 2 and that the halogen deactivating effect in 1 is similar to that in thiophene. 

Methyl 4,5,6,7-tetrafiuorobenzo[h](hiophene-2-carboxylate is oxidized by trifluoroperacetic acid or m-CPBA to form a 2,3-epoxysulfbne reaction with chlorine or sulfuryl chloride produces a 2,3-dichIoride derivative <94JFCS1>. HOF MeCN is a novel oxidant which oxidizes a variety of thiophene derivatives to 3,5-dioxides <94CC1959>. Bromination of thieno[c]fused l,S-n hthyridines occurs with tetrabutylammonium perbromide <94H331> or with dibromoisocyanuric acid/sulfuric acid <94JHCS21>. 

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