Thiophene moieties

Structure-activity studies of 5,6,7,8-tetrahdyro-5,5,8,8-tetramethyl-2-quinoxaline derivatives necessitated the preparation of thiophene-containing compound 17. Stetter conditions using thiazolium salt 20 as catalyst resulted in the preparation of 1,4-diketone 21 from 18 and 19. Condensation of 21 with phosphorus pentasulfide followed by saponification resulted in 17. In this fashion, the authors replaced the amide linker of parent compound 22 with the rigid thiophene moiety. 

Another ligand including a thiophene moiety but lacking the C2-symmetry and thus bearing electronically different phosphorus atoms was prepared by these authors, in 2001. The electrochemical oxidative potential was obtained by cyclic voltammetry. The oxidation potential of the phosphine group located on the phenyl ring was found to be 0.74 V (vs. Ag/Ag" ) and the authors attributed a value of 0.91 V to the phosphine attached to the thiophene moiety. This second functionality is a rather electron-poor phosphine. As shown... 

Jen et al. have investigated a copolymer PAE comprising electron-accepting 9,9-bis(2-ethylhexyl)-2,7-diethynyl fluorene and hole-transporting thiophene moieties in an alternating fashion (Table 3, entry 12) [119]. The design was based on the assumption that the combination of fiuorenyl and thiophene moieties would lead to a balanced transport of electrons and holes. The sterically hindered substituents were introduced with the hope that they would prevent intermolecular interactions and, thus, keep the PL quantum efficiency high. 

The dimer heated with dimethylacetylene dicarboxylate (DMAD) gives the adduct D, resulting from the addition to the tellurophene moiety of A. The adduct E resulting from the addition to the thiophene moiety of A was not detected. 

Typical syntheses of unsymmetrical derivatives include 27 (98CL1123), 28 (08SA1065), and 29 (Scheme 10). The perfluorocyclopentene fragment in the latter compound is bound to different positions in the thiophene moieties (95CL969, 04CC1010). 

In a subsequent study by Robertson, Murphy, and coworkers, polymer 23 was synthesized by anodie polymerization on platinum electrodes and eompared to polymer 19 in order to determine the effect of the position of the linkage of the dithiolene to thiophene moieties. In this study, the researchers used the salts [Bu4N][ll] and [Bu4N][16] in MeCN to prepare the respective polymers 19 and 23. Surprisingly, the polymerization of the anion 11 resulted in films exhibiting different electroehemieal response than that observed for 19... 

Substitution of the 1,4-phenylene unit with 2,5-thiophene has also been investigated as a backbone deviation in PBZT [49] and PBZO [50] systems. A catenation angle of 148° was introduced in both systems resulting in anisotropic reaction mixtures at concentration above 10% by weight. Evers et al. polymerized the mono, di and tri-thiophene moieties as diacid chlorides with l,4-dimercapto-2,5-diamino-1,4-benzene dihydrochloride in PPA to give polymers with intrinsic viscosities in the range of 5-8 dL/g. All these materials... 

The chemistry of thienopyridazines has not been investigated in great detail. Nitration of thieno[2,3-d]pyridazine (311) occurs in the thiophene moiety at C-3 with 61.5% yield. 

Electrophilic and nucleophilic reactions of 2-(2-thienyl)thieno[2,3-cf pyrimidine (346), prepared as shown in Scheme 99, permits a conclusion concerning the reactivity compared with that of thiophene bearing an electron deficient substituent in position 2. Both nitration and bromination primarily occur in the thiophene moiety whereas lithium organic reagents (methyllithium, butyllithium) add at carbon atom 4 (77BSF676). Bromination of (324) yields the 5- (or 6-) bromo derivative (68CR(C)(267)697). 

The foregoing results are entirely in accord with the assumption that the thieno[3,4-c]thiophene moiety is a delocalized system, dienophile addition occurring in both cases at the ring with highest electron density (75ACR139, 77HC(30)317). 

The theoretical study of thicno[3,4-z/ thiepine 15 and furo[3,4-rf thiepine 16, as dienes in thiophene or furan moieties, respectively, in the Diels-Alder reaction was investigated with semi-empirical AMI calculations <1995JHC1499>. S-Methylation at the thiophene moiety of thieno[3,4-t/]thiepine 15 was predicted to lower the activation energy and facilitate reaction with less reactive dienophiles, such as ethylene. 

Vamvounis and Holdcroft prepared a series of fluorene-thiophene copolymers 579 with a varying ratio of conjugated (2,5-thienylene) and nonconjugated (3,4-thienylene) thiophene moieties in the polymer chain (04AM716). The PL efficiencies in films are low (6 and 7%, respectively). Substantial increases in solid-state PL efficiencies were observed reaching a value of 43% for copolymer 579e. 

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