3-Bromo-2-nitrobenzo thiophene

On the basis of labelling studies it has been concluded70 that an intermediate of the type (53) must be involved in the reaction of 3-bromo-2-nitrobenzo[ ]thiophene (52) with 3-(trifluoromethyl)aniline in order to account for the observed labelling patterns in the products (54) and (55). 

Mononitration of benzo[6]thiophene gives a complex mixture in which the 3-isomer predominates (73% in acetic anhydride at 25 °C) and can be separated from other isomers, which may include 4-, 5-, 6- and 7-nitro derivatives. However, benzo[6]thiophenes with electron-donating groups at the 3-position, e.g. 3-methyl-, 3-acetamido- or 3-bromo-benzo[6]thiophene, are nitrated almost exclusively in the 2-position. 2-Nitro-benzo[6] thiophene may be prepared by debromination of 3-bromo-2-nitro-benzo[6 ]thiophene, or by decarboxylation of 2-nitrobenzo[6]thiophene-3-carboxylic acid (70AHC(11)177). 

The Hunsdiecker reaction has been used only twice as a potential source of bromobenzo[6]thiophenes with 3-bromo-5-nitrobenzo[6]-thiophene-2-carboxylic acid it proceeds normally to give 2,3-dibromo-5-nitrobenzo[6]thiophene,152 but with 5-nitrobenzo[6]thiophene-2-carboxylic acid the main product is 3-bromo-5-nitrobenzo[6]thio-phene-2-carboxylic acid, accompanied by smaller amounts of 2,3-dibromo-5-nitrobenzo[6]thiophene.152 497... 

Sulfonation of 4-nitrobenzo[6]thiophene gives the 3-sulfonic acid in low yield.84 Sulfonation of 3-nitro- and 3-bromo-2-nitrobenzo[7>]-thiophene gives in each case a monosulfonic acid of undetermined structure.694... 

The compounds (535) and (536) have been prepared through the condensation of 3-bromo-3-methyl-2-butanone with 2- and 3-thienylammonium hexachlorostannates in the presence of zinc chloride. Benzo[A]thieno-[3,2- )]indoles (537) have been prepared by reductive cyclization of 2-aryl-3-nitrobenzo[6]thiophens with triethyl phosphite. The parent heterocycle was also obtained from 2-(o-nitrophenyl)benzo[6]thiophen with triethyl phosphite and by heating 3-azido-2-phenyl- or 2-(o-azidophenyl)-benzo[6]-thiophen in diglyme. ... 

Pyrazole-, Thiazole-, and Imidazole-fused Thiophens and Related Systems.— The behaviour of thieno- and selenolo-t-3,2-i/]pyrazoles in formylation and bromina-tion reactions has been studied. In contrast to benzo[fe]thiophen, a substituent is directed into the a-position of the condensed thiophen ring. 2-Mercapto-thieno[3,2-prepared from 2-chloro-3-nitrothiophen and sodium disulphide followed by carbon disulphide. A benzo-fused system was prepared similarly from 3-bromo-2-nitrobenzo[6]thiophen. Derivatives of... 

Nucleophilic Substitution, Metallation, and Halogen-Metal Exchange.—Direct nucleophilic displacement of the 7-chloro-group of 7-chloro-3-methyl-benzo[b]thiophen has been achieved. 3-Bromobenzo[b]thiophen was reduced to the 3-deuterio-derivative by the reaction with sodium borodeuteride and palladium chloride. Meisenheimer complexes were formed in the reaction of methoxide ion with 2-methoxy-3-nitro- and 3-methoxy-2-nitrobenzo[b]thiophen. Rate and equilibrium data were determined in methanol at 25 C. On treatment of 2-bromobenzo[b]thiophen with potassium amide in liquid ammonia, bromine migration to the adjacent carbon atom was observed. Considerable evidence for the occurrence of an intermolecular transbromination was obtained. The reaction of 3-bromo-benzo[b]thiophen with piperidine has been reinvestigated and found to give primarily the normal, but also some of the cine-substitution product, which is the only product obtained in the reaction of 2-bromobenzo[b]thiophen. Possible mechanisms for some of these reacticms are suggested. 

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