Heterocycles dihydrobenzo thiophene

The principal mechanisms proposed for the heterogeneous HDS of a prototypical 5-heterocycle, namely benzo[6]thiophene (BT), are illustrated in Scheme 1. The plain hydrogenation of C-C double bonds occurs in step a, involving the regiose-lective reduction of BT to dihydrobenzo[/ ]thiophene (DHBT), as well as in step e, where styrene is reduced to ethylbenzene. 

For benzo[Z ]thiophene the heterocycle is rather more resistant to ring opening and oxidation with hydrogen peroxide in acetic acid at 95 C, for example, gives the 1,1-dioxide (Scheme 7.22) reduction with either sodium and ethanol or triethylsilane in trifluoroacetic acid affords 2,3-dihydrobenzo[Z)]thiophene. Electrophiles give mainly 3-substituted benzo[Z ]thiophenes, although these products are often accompanied by smaller amounts of the 2-isomers. 

Of the analogous parent heterocycles, benzo[c]pyrrole (isoindole),2 benzo[c]furan, and benzo[c]thiophene, only the last has proved sufficiently stable for isolation (see Sections II and IV). Although the first reference to the benzo[c]thiophene system in the literature was Leser s3 synthesis of l,3-dihydrobenzo[c]thiophene in 1884 (Section... 

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. 

Hydroxymethyl-5,6-methylenedioxybenzo[b] thiophene refluxed 4 hrs. in di-methoxyethane containing some polyphosphoric acid 6,12-dihydrobenzo-[1,2-b 4,5-b ]bis-5,6-methylenedioxybenzo[b] thiophene. Y 75%. E. Campaigne and E. S. Neiss, J. Heterocyclic Ghem. 2, 100 (1965). 

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