Azuleno thiophenes

Azuleno(l,2-b)thiophene [25043-00-9] M 184.2. Crystd from cyclohexane, then sublimed in vacuo. 

Thioacetamide has been utilized as a sulfur transfer reagent in the synthesis of azuleno[l,2-c]thiophenes <02H(58)405>. 

Various Carbocycle-fused Systems.- Azuleno[2,l-fc]thiophens have been prepared from ethyl 2-chloro-3-formylazulene-l-carboxylate and ethyl mercaptoacetate. The reaction of (261) with sulphur in quinoline gave (262). It is claimed that, in the cation of (263), the charge is largely localized on the carbon atom that is flanked by the two thiophen rings. 

Aza-azuleno[2,l-b] thiophen has been prepared from 2-chloro-3-formyl-l-aza-azulene by annelating the thiophen ring by the Fiesselmann reaction. ... 

J With enamines. l-Oxa-2-azulenones (as tethered heptafulvenes) with enamines undergo [8+2] cycloaddition as well (85HOU(5/2c)127, p. 218 98SL950). This way, in the case of heterocyclic enamines (such as 40), azuleno[l,2]-fused azoles and azines are formed (Schemes 13 and 14) The reactions of oxaazulenone 37 with the isomer mixtures of enamines 40a or 40b yield mixtures of isomeric dihydrothiophenes 41 and 42 that are dehydrogenated by 2,3-dichloro-5,6-dicyano-p-benzoqui-none (DDQ) to yield thiophenes 43 and 44, respectively (83CL1721). Whereas the latter [l,2-c]-fused compound is unstable because of its o-quinonoid structure, thiophenes 43a and b are demethoxycarbonylated to yield substances 45a and b. 

Analogous reactions lead to acylvinyl derivatives (t3 es 55a-55e) of azuleno[2,l-b]thiophene (02T7653), azuleno[l,2-b]- and azuleno[2,l-fc]-benzothiophene (04OBC1413), and azuleno[2,l-b]indole (06TL8535, 07H(74)951), respectively, and the corresponding azuleno[l,2-b]indole derivatives (07H(74)951). 

In contrast, azuleno[l,8-fcc]thiophene 179c is generated by the acid-catalyzed cyclodehydration of sulfine 179a and demethylation of the resulting sulfenium salt 179b (71JA2196). 

The stability of azuleno[l,2-l ]- and azuleno[2,l-fc]thiophene (45a and 69, respectively) is comparable to that of benz[a]azulene because the computed heats of formation of all three of them range from about 102 to 104kcal/mole (83JF2,1155). In the groups of simple iso-7t-electronic azuleno[l,2-b]-, azuleno[2,l-fc]-, and azuleno[l,2-c]azoles, the stability has been predicted to decrease in the order of fused (benzene >) pyrrole > thiophene > furan, that is in the order of the stabilities of the heterocyclic moieties (87H(26)2025). Non-functionalized azuleno[6,5-b]pyrrole 195 is... 

Azuleno(2,l-b)thiophene [248-13-5] M 184.2. It is crystallised from cyclohexane, then sublimed m vacuo. 

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