Thiophenes 3-bromo-, from 2-bromothiophene

Halothiophenes, which are not activated through the presence of —I—M-substituents, undergo substitution smoothly under more forcing conditions with copper salts in pyridine or quinoline. Hence 3-cyanothiophene and 5-methyl-2-cyanothiophene have been obtained from the corresponding bromo compounds. 2-Bromothiophene reacts readily with aliphatic cuprous mercaptides in quinoline at 200°C to give thioethers in high yields. The use of the copper-catalyzed Williamson synthesis of alkoxythiophenes from iodo- or bromo-thiophenes and alcoholate has been mentioned before. The reaction of 2-bromothiophene with acetanilide in nitrobenzene in... 

The preparation of thieno[3,2-fc]thiophene was reported by Iddon and co-workers [76, 77] and it is readily prepared in four steps from commercially available 3-bromothiophene (Scheme 17.1). Thus 3-bromo-thiophene can be lithiated in the 2-position with a bulky non-nucleophilic base such as lithium diisopropylamine. Quenching of the resulting thiophene anion with dimethylfonnamide or tV-formylpiperidine afforded the thiophene aldehyde. Treatment of this o-bromoaldehyde with ethyl 2-sulfanylacetate in the presence of base afforded thieno[3,2-fc]thiophene carboxylate ester in good yield. Hydrolysis of the ester group, followed by thermal decarboxylation of the resulting acid with quinoline in the presence of copper, afforded the unsubstituted thieno[3,2-f>]thiophene in overall yields of approximately 60 % over the four steps. 

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