Thiophenes substitution

Thiophenes substituted with groups such as alkyl, halogens, OCH3, and SCH3 show small but characteristic differences between 2- and 3-substituted compounds. In these cases, however, it is the 2-isomer which shows the less complex spectrum. Thus, 2-substituted alkylthio-phenes and halothiophenes show a single band with greater extinction than the 3-isomers whose spectra exhibit two peaks in a broadened absorption band. These differences are also present in the spectra of 2,5- and 3,4-dihalosubstituted compounds. In 2-substituted thiophenes, the intensity of the band varies inversely as the electronega-... 

As we found that furan and thiophene substituted oximes can be used as substrates for the INOC reactions (Eq. 5) [29b] similarly, furan substituted nitro alkane 134 is also a good substrate for INOC reactions (Eq. 13) [40]. The furfuryl derivative 134, prepared via Michael addition of furfuryl alcohol to 4-methoxy- -nitrostyrene, was subsequently transformed without isolation of the intermediate nitrile oxide 135 to the triheterocyclic isoxazoline 136 as a 5 1 mixture of isomers in high yield. 

Similarly, the thiophene-substituted cyclopropyl ketone 1-65 led to the fused ben-zothiophenes 1-67 and 1-68 as a 2 1 mixture. In this process the intramolecular interception of the cationic intermediate 1-66 took place at C-3 and C-5 of the ben-zothiophene moiety (Scheme 1.18). 

In the case of catalyst 3, the thiophene substitution in the 6,7 position controls the gap aperture between fluorenyl and indenyl ligands by repulsing steric interactions at the complex backside [10, 11]. This leads to increased stereoselectivities [9] and is responsible for a C2-symmetric-like polymerization mechanism, characterized by increasing isotacticities when the polymerization temperature is reduced [5, 11] (Fig. 7). 

A study of reactions of NBS in acetic acid and acetic anhydride with thiophenes substituted in the a-position by groups such as 4-thiazolyl or 2-quinolinyl demonstrated that after initial perbromide formation (at around 20°C), slow conversion into C-brominated products followed. Reactions carried out above 40°C with one molar equivalent of NBS gave 5-bromo products only, but introduction of electron-donating groups into the thia-zole substituent and excess brominating agent led to some thiazole bromi-nation. With a 2-aminothiazolyl substituent, bromination took place exclu-... 

The question of intermediates in thiophene substitutions may not always be so straightforward as portrayed so far. The sulfur atom itself can be the site of attack by an electrophile, i.e. (14) and also Section 3.13.2.4. One can postulate that selectivity in thiophenes could result from attack of an electrophile, for example a halonium ion, at sulfur followed by 1,5-sigmatropic rearrangement and deprotonation as shown in equation (6). A determination of the relative stabilities of (23) and (17) for different substituents X is needed for assessment of the validity of this possibility. Note that the rearrangement type represented by (23) to (17) is known in a photochemical variant (equation 7) (73TL3929). From ab initio calculations on thiophene it also appears that initial attack of an electrophile on sulfur is the pathway of higher electron density (72MI31302). 

Same authors further synthesized (1-thiophene-substituted 21,23-dithia and 21-thiaporphyrins. The 21,23-dithia 240a and 21-thiaporphyrin 241a having a methyl and phenyl group at (5-positions of thiophene were synthesized by condensing the 3,4-disubstituted thiophene diols 239a (Scheme 95) with... 

Scheme 95 Synthesis of fi-thiophene-substituted 21,23-dithia and 21-monothiaporphyrin.

Even in these relatively sulfur-lean samples, organic sulfur pyrolysis products are detected throughout the maturity range studied. The FPD chromatogram of the most immature sample is dominated by C -C alkylthiophenes. Compared to a wide variety of kerogens, pyrolysates of the Mahakam coals tend to contain relatively high amounts of thiophenes substituted at positions 3 and 4 (61). 

Of particular interest is the identification of five different types of heterocyclic sulfur-containing flavor components, the preponderance of which were furans and thiophenes substituted with sulfur in the 2- and 3-position. The bulk of these flavor compounds had not been identified in meat and had not been reported in the literature so far. These sulfur-substituted heterocyclic flavor components will be further discussed below. 

FURANS AND THIOPHENES SUBSTITUTED AT THE THREE POSITION WITH SULFUR... 

C. Moustrou, A. Samat, R. Guglielmetti, R. Dubest, and F. Gamier, Synthesis of thiophene-substituted spiropyrans and spirooxazines precursors of photochromic polymers, Helv. Chim. Acta 78, 1887-1893 (1995). 

M. Tiecco and A. Tundo, Int. J. Sulfur Chem. 8, 295-306 (1973). Thiophenes, substitution reactions ... 

Strecker synthesis attempts have been made to optimize the reaction conditions [4b] and to achieve stereoselective syntheses [4c-hJ. Usually chiral amines such as 7 have been employed, which can, for example, on reaction with 6 be converted to the thiophene-substituted amino acid 8 [4c]. 

Aroyl- and thiophene-substituted pyrrole derivatives, for example, 45 (R = FI, Me, Et Ar = Ph, 2-thienyl, 4-CIC6H4, etc. Ar = Ph, 5-chloro-2-thienyl, 4-CIC6FI4, etc.) have been synthesized as a new class of COX-l/COX-2 inhibitors <2000EJM499>. iV-(Pyridin-3-ylmethyl)-3-[5-chloro-l-(4-chlorobenzyl)indol-3-yl]propanamide 46 represents one of the most potent compounds evaluated in the 12-0-tetradecanoylphorbol-13-acetate (TPA)-induced mouse ear swelling assay, with a level of activity higher than that of ibuprofen and comparable to that of dexametha-sone <2004BML5441>. 

Complete assignment of the chemical shifts of thiophene-substituted -xylenes by different NMR techniques... 

With a view to preparing polymerizable complexes, thiophene-substituted nickel-dithiolene complexes [Ni(L)(L )] have been synthesized and used to prepare films by electrochemical polymerization. The features of the complexes and of the polymers depend on the number of thiophene substituents. In particular, the complex with four thiophene substituents (L = L = thpdt, 12) shows a narrower HOMO-LUMO gap as compared to complexes with two thiophene and two phenyl groups or four phenyl groups [Xmax, nm (e, M- cm- ) 976 (38800) L = L = 12 931 (37700) L = 12, L = 9, R = Ph 866 (30900) L = L = 9, R = Ph] and gave a polymer whose electrochemical features are similar to those of poly[l,2-di(2,5-thienylene)ethane], suggesting that similar extended chains are formed"". 

Despite the proven depressant neurotropic influence of furan- or thiophene-substituted germa-tranes, germatranes and stannatranes have been studied to develop routes for their synthesis, from triethanolamine or tristannyl ethers "" their substitution reactions, their structures, " and iododestannation. ... 

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