1.3.4.6- Tetra thieno thiophenes

The reduction of thieno[3,2-6]thiophene-2,5-diaIdehyde or dithieno-[3,2-i 2, 3 -d]thiophene-2,6-dialdchyde with potassium in tetra-hydrofuran or 1,2-dimethoxyethane yields the corresponding anion-radicals, the ESR of which give information on the conformation of similar carbonyl compounds.Cation-radicals have also been studied (see Section IV). 

Dim yl-l/f,3/f-thieno[3,4-c]thiophene (142) with sodium periodate in methanol yields e 2-oxide (143) (91%X and 1,3,4,6-tetra-phenyl-lfl, 3fl-thieno[3,4-c]thiophene (147) behaves analogously to form 148 (96%). 

The tetrahydrobenzo[4,5]thieno[2,3-Z>]pyridine 48 was easily obtained from tetra-hydrobenzo[b]thiophene 49, methyl acetoacetate (or ethyl acetoacetate) and stannic chloride (2005MI1). 

In the presence of triphenyl- or tributylphosphine, 2,3-di(alkylthio)cycloprope-nethiones 96 are dimerized (refluxing in benzene under nitrogen, 4h) to 1,3,4,6-tetra(alkylthio)thieno[3,4-c]thiophenes (97) in moderate yields (85JA5801, 88JHC559). The authors also demonstrated that thienothiophene 97 (R = R = Pr ) is involved in a cycloaddition with dimethyl acetylenedicarboxylate (98) to form 5,6-dimethoxycarbonylbenzo[c]thiophene (99). 

Dinitrile 118 was also used in the synthesis of other thieno[2,3-Z ]thiophene derivatives (86MI1). Various tri- and tetra-substituted thieno[2,3- ]thiophenes were prepared according to modifications (74T93, 80ZC96, 92LA387, 95CCC1578). 

As mentioned above, thieno[3,4-c]thiophene is most difficult to synthesize compared to all other isomeric thienothiophenes. A few of its derivatives are known tetraphenyl- (67JA3639, 73JA2558, 73JA2561), tetrakis(alkylthio)- (85JA5801), tetra(2-thienyl)- [42], tetrabromo-, l,3-dibromo-4,6-dicyano-, l,3-dibromo-4,5-bis (methoxycarbonyl)- (94JOC2223), l,4-bis(rert-butylthio)-3,6-diphenyl- and 3,6-di (2-thienyl)thieno[3,4-c]thiophenes (98JOC163). 

The UV spectra of 3,6-dimethylthieno[3,2-Z)]thiophene, 3,6-dimethylselenolo [3,2-Z ]selenophene, their dimers, trimers and tetramers (96T471), 2,2,5,5-tetra-methylthieno[3,2-Z ]thiophene-3,6-dione (68TCA247, 77CB1421), and derivatives of benzo[ )]thieno[3,2-Z ]benzo[ )]thiophene 121 (80ZOR425) and compounds 300-305 (93JOC5209) were measured and analysed. 

A system with four alkylated thieno[3,2-b]thiophenes, located around a benzene through ethylene linkages, depended for its synthesis on the reaction of aldehyde (82) with [l,2,4,5-tetra(diethoxyphosphorylmethyl)benzyl]phosphonic acid diethyl ester (83) (Scheme 20) [41]. 

The synthesis of 231 was achieved in three steps starting from 1,1,2,2-tetrabenzoylethane (232) thus double ring closure using P4S10 [89], produced 233, treatment with NaI04 then yielding the sulfoxide 234 and dehydration with acetic anhydride furnished 231 (Scheme 56) [86, 87]. Tetra(thien-2-yl)thieno[3,4-c] thiophene (237), a dark purple (Amax 576 nm), stable crystalline substance, was made in similar fashion (Scheme 57) [12]. 

Electron-deficient thiophene-based monomers including thieno[3,4-c] pyrrole-4,6-dione (TPD), furo[3,4-c]pyrrole-4,6-dione (FPD) monomers, diketopyrrolopyrrole and isoindigo can be copolymerized with bromi-nated thiophene-based electron-rich monomers such as benzodithiophene, dithienosilole, and dithienogermole by direct arylation polymerization. Additionally, electron deficient 4,4 -dinonyl-2,2 -bithiazole and 1,2,4,5-tetra-fluorobenzene are highly reactive toward direct arylation polymerization. ... 

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