Benzothiophenes acids/ketones

A recent report indicates that thiophenes (not benzothiophenes) may be formed from alkyl phenyl ketones by treatment with a slight excess of thionyl chloride in the cold.58 Propiophenone, for example, yields 3,4-dibenzoyl-thiophene (47). Adipic acid and related carboxylic acids yield thiophene derivatives upon treatment with thionyl chloride in the presence of pyridine.59... 

Cyclisation of 2-arylthio- or 2-aryloxy-aldehydes, -ketones or -acids via intramolecular electrophilic attack on the aromatic ring, with loss of water, creates the heterocyclic ring this route is a common method for the ring synthesis of benzothiophenes. 

Comparable acid- (or Lewis acid) -catalysed ring closures of 2-arylthio- and 2-aryloxy- -ketones, and -2-arylthio- and 2-aryloxyacetyl- chlorides lead to 3-substituted heterocycles and 3-oxygenated heterocycles, respectively. It is possible to combine the preparation of the arylthio-ketone and the ring closure steps utilising two solid-supported reagents in a one-pot procedure, as illustrated. Formation of 3-aryl-benzothiophenes by this route can be complicated by partial or complete isomerisation to the 2-aryl-heterocycle,however using boron trifluoride as the Lewis acid produces only the 3-aryl-isomer. 3-Tosylamino-benzofurans can be prepared from aryl glyoxal hydrates. ... 

Intramolecular aldol/Perkin type condensation of orf/to-formylaryloxyacetic acids and arylthioacetic esters produces benzofuran- and benzothiophene-2-esters respectively, as illustrated below. The synthesis can be performed in one pot, thus ortfto-hydroxyaryl-aldehydes or -ketones, are 0-alkylated with a-halo-ketones, then intramolecular aldol condensation in situ produces 2-acyl or 2-aroyl-benzofurans. ° For benzothiophenes, the ring-closure substrates can also be obtained via methyl thioacetate displacement of fluoride from orf/to-fluoro-araldehydes. ... 

Further details of the rearrangement-ring contraction of the ketone ArSCMeaCHaCOMe, which gives benzothiophens with polyphosphoric acid, have been reported. Additional analogues of thiochroman clathrate hosts have been prepared in order to test their inclusion properties. The thermolysis of 2,2-dimethyl-l-(toluene-/j-sulphonylimino)thiochroman has been investigated. In benzene it gives A -[2-(3-methylbut-3-enyl)phenylthio]-iV-(2 -methyI-thiochroman-2 -ylmethyl)toluene-p-sulphonamide. 

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