Thieno-thiophenes acylation

O-Acyl derivatives of thiohydroxamic esters (Barton esters) react with benzynes to afford a tricyclic thiophene ring system thus the pyridine derivative 30 gives benzo[4,5]thieno[2,3-A pyridines 31 (Scheme 14) <2002JOC3409, CHEC-III(3.11.3.3)900>. 

A similar mercaptoacetate addition reaction to 5-acyl-4,7-dioxo-4,7-dihydrobenzo[i]thiophene-2-carboxylates followed by cyclization and oxidation to give benzo[ 1,2-6 5,4-ft ]dithiophene-4,8-dione derivatives 29 has been shown <03H1689>. Nitrogen bridged heterocycles, 3-(benzylthio)thieno[3,4-6]indolizine derivatives 30 have been synthesized and intramolecular arene-arene interactions within these compounds were reported <03CPB75>. The arene-arene interaction leads to significant shifts in the proton NMR signals and red shifts in the absorption maxima. 

Acylation of 3-acetonyl-5-alkylthieno[2,3-fe]thiophenes 208 and 3-acetonyl-5-methylthieno[3,2-fe]thiophenes (209) in a mixture of aliphatic acid anhydride and perchloric acid (actually, acylium perchlorate) was demonstrated (79KGS1424) to occur at the free a position followed by cyclization and formation of perchlorates of tricyclic pyrylium salts 210 and 211 (yields > 80%). The latter are transformed into thieno[2, 3 5,4]- (212) and -[2, 3 4,5]thieno[2,3-c]pyridmes 213 in yields higher than 90% by passing ammonia through their suspensions. 

Skraup and Conrad-Limpach reactions to appropriate benzo[6]thiophen derivatives. Substitution reactions of thieno[3,2-/]quinoline (559), which was prepared by a Skraup synthesis from 5-aminobenzo[6]thiophen, have been studied. The same method has also been used earlier for the synthesis of the 7- and 9-methyl derivatives of (559). Nitration, bromina-tion, and acylation of (559) occur in the 2-position. Some reactions of... 

Smutny. The t-butyl ester was used in order to achieve hydrolysis of (30), which required reaction with trifluoroacetic acid at 0 °C for 4—5 h. Treatment of (30) with warm trifluoroacetic acid for 10 min yielded (31). The reaction of (29) with ethyl a-chloroacetate gave (32). A-Phenyl phenylpropynthioamide (33) reacts in a similar manner with active bromomethylene derivatives, such as bromo-acetonitrile, bromonitromethane, and /j-nitrobenzyl bromide, in the presence of triethylamine to give the thiophen (33a). Instead of enamine thioesters such as (29), 2-aminovinyl thioketones (34) react with a-bromo-ketones in the presence of triethylamine to give 2-acyl-thiophens (35). By the ion-pair extraction method, tetrabutylammonium salts of acetylacetone were allowed to react with carbon disulphide to give (36), which upon reaction with chloroacetone gave a 45% yield of the thiol (37), in addition to a thieno[2,3-A]thiophen derivative. ... 

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