Thiophene core-substituted

This section discusses the inhibition phenomenon with specific reference to its influence on the conversion rates of dialkyldibenzothiophenes. The kinetic description of inhibition effects of even the parent molecule, thiophene, is quite complicated, and the complications become even greater as the thiophene core is fused to other aromatic rings and/or substituted with alkyl groups. In commercial processes the fact that there are many different sulfur species that are simultaneously being converted makes describing inhibition with a single equation an almost impossible task. A particularly relevant comment to this effect was made by Stanislaus and Cooper and is quoted here (109). ... 

While the incorporation of these solublizing groups at the 3-position has yielded PTs that have surmounted the intractability issue and also contain fewer (3-defects, such substitution of the thiophene core necessarily results in the loss of ring symmetry. With these functionalized monomers, two different types of a-linkages now exist since the 2- and 5-positions are no longer equivalent [231, 232]. 

The oligothiophenes 27 bear phenyl groups in the 3 -position of the thiophene cores that are para-substituted with electronically diverse functional groups (R = CF3, H, CH3, OCH3). Here, the phenyl spacers enhance the solubility of the oligomers and warrant the electronic communication between the elements of diver-... 

Oligothiophenes substituted by terminal alkoxy-chains exhibit a peculiar phenomena of differential mobility between the core and the chain ends. In fact, the chain ends present gauche conformations that slow down their motion. On the contrary, the thiophene core, appended to the alkoxy plugs, shows exceptionally high librational mobility in both the ground and excited states as a molecular gyroscope [60]. 

A one-pot synthesis of 4-substituted 3-amino-2-cyanothiophenes involving o-ethyl thioformate was reported (140L2522). The thiophene core in these 4-subsitututed 2-cyanothiophenes can be readily incorporated into more elaborate pharmaceutically relevant structures as... 

Thiophene, another r-excessive heterocycle, was originally used in the Blanc reaction in 1942 by Blicke and Burckhalter. Following then-procedure, a large scale synthesis of 32 has been developed. Notably, in reaction with un-substituted thiophene (31), the chloromethyl group is selectively installed at the 2-position. This particular chloromethylation has been frequently used as a method for incorporation of the thiophene core into other molecules. ... 

The versatility of poly(phenylcne) chemistry can also be seen in that it constitutes a platform for the design of other conjugated polymers with aromatic building blocks. Thus, one can proceed from 1,4- to 1,3-, and 1,2-phenylene compounds, and the benzene block can also be replaced by other aromatic cores such as naphthalene or anthracene, helerocyclcs such as thiophene or pyridine as well as by their substituted or bridged derivatives. Conceptually, poly(pheny ene)s can also be regarded as the parent structure of a series of related polymers which arc obtained not by linking the phenylene units directly, but by incorporation of other conjugated, e.g. olefinic or acetylenic, moieties. 

It is assumed that the heterocyclic core structure is responsible for the appropriate orientation of the aromatic rings in space and finally for binding to the enzyme. A wide variety of heterocycles can serve as templates, i.e. pyrrole, thiazole, oxazole furane, furanone, imidazole, isoxazole, pyrimidine and thiophene, but at the moment pyrazole and cylopentenone seem to be the most appropriate for achieving COX-2 specificity. For optimal activity, one aromatic ring must be substituted with a methylsulfonyl or a sulfonamide substituent in the para position. Substitution at position 4 of one of the aromatic systems with a sulfonamide or a methylsulfonyl group is essential for COX inhibition. Replacement of the methylsulfonyl group by a sulfonamide group reduces COX-2 selectivity but improves oral bioavailability. 

The XPS Cls and S2p core-level lineshapes for the thiophene oligomers, thiophene polymers and alkyl-substituted thiophene polymers are well documented in the literature [117,123—126]. Table 3.4 summarizes the Cl s, S2p BE values, their linewidths (full width at half maximum, FWHM) and the S/C atomic ratios for several thiophene oligomers and polymers [117]. In general, the a and p carbons in thiophene polymers with a BE separation of only 0.34 eV cannot be resolved from the main Cls component. Two other minor Cls components located at above 2.6 eV and 5.2 eV above the main peak have been assigned to the shake-up structures. The S2p core-level spectrum is curve-fitted with two components with BEs at about 163.8 and 165.5 eV, corresponding to the respective spin-orbit split doublets (S2p3/2 and S2pi/2). An n transition shake-up structure is also discernible at... 

The introduction of kinked linkages into the polymer backbone effectively reduces the regularity of the molecule and lowers the melting temperature. However, the incorporation of kinked units has an unfavorable influence on the liquid crystallinity because the kinks disrupt the molecular linearity. Frequently used kinked monomers include isophthalic acid (with the meta linked core angle of 120°), 2,5 substituted thiophene (with a core angle of 148°), and so on. The induction of kinks into the molecular chain tends to lower the thermal stability of theLCPs [4,19]. 

An isomer of TTC 4.34, in which the macrocycle is built up from 3,4-substituted thiophene units, was synthesized by the same group with the aim of developing liquid crystalline materials, in particular discotic mesogens. 2,5-Alkynylated 3-ethynyM-iodothiophenes were cycUzed with the catalytic system Pd /Cu(I) to give colorless cyclotriynes 4.36 in yields up to 25 % (Scheme 1.46). An X-ray structure analysis of one derivative showed that in the crystal the cyclotriyne cores do not interact [411]. 

Wynberg and co-workers have prepared helicenes composed of fused thiophene and benzene units from the photocyclization of alkene precursors [134], It was shown that the effect of substituting thiophenes for benzene rings in these structures led to a blue shift of the absorption maxima. Compound 61 can be converted to the circulene structure 62 in two steps and the latter compound represents another interesting class of fused thiophene stmctures [135]. Trithiophenes with a benzene core (63) can be prepared from diacetylene-fimctionalized bithiophenes via a five-coordinate rhodium(I) intermediate by the addition of elemental sulfur [136]. A related structure (64) was reported by Pei et al. [137], along with the elaborate helicene 65. The compounds were constracted via oxidative (FeCb) cyclization reactions of 1,2-dithienyl benzene derivatives. 

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