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Thiophenes oxidative coupling

Silver salts have been used extensively as oxidants in many different types of biaryl CDC reactions, such as the arylation of indoles, " " azoles, thiophenes," " chromones, xanthines," uracils," and pyridine-iV-oxides." " " They are also used in the inter- and intramolecular coupling of simple arenes. ° Recently, Zhang and co-workers oxidatively coupled thiophene derivatives and fluorinated arenes, using only 2.5 mol% of Pd(OAc)2 as a catalyst and AgCOs as an oxidant (Scheme 6.8)." " ... [Pg.121]

The oxidative coupling of thiophene, furan[338] and pyrrole[339,340] is also possible. The following order of reactivity was observed in the coupling of substituted furans[338] R = H > Me > CHO > CO Me > CH(OAc)i > CO2H. The cross-coupling of furans and thiophenes with arene is possible, and 4-phenylfurfural (397) is the main product of the cross-coupling of furfural and benzene[341]. [Pg.75]

Polyheterocycles. Heterocychc monomers such as pyrrole and thiophene form hiUy conjugated polymers (4) with the potential for doped conductivity when polymerization occurs in the 2, 5 positions as shown in equation 6. The heterocycle monomers can be polymerized by an oxidative coupling mechanism, which can be initiated by either chemical or electrochemical means. Similar methods have been used to synthesize poly(p-phenylenes). [Pg.36]

Cyclic voltametric analysis has been utilized to determine material properties of this class of heterocyclic compounds. All the DTPs 23 <2003JOC2921 > exhibited a well-defined irreversible oxidation presumably corresponding to the formation of the radical cation. When scanned to higher positive potentials, it resulted in two consecutive broad oxidations for most of the DTPs. The second oxidation is quite weak, followed by a more intense and well-defined third oxidation. Coupling of thiophene radical cation is usually rapid (r <10-5 s) <1995SM(75)95>. These additional broad waves most likely correspond to the oxidation of coupled products rather than further DTP oxidations. The electrochemical data of the DTP S 23 are given in the Table 10. [Pg.646]

An improved synthesis of dithieno[3,2-A2, 3 -<7]thiophene 15a has been achieved from 2,3-dibromothiophene 304 (Scheme 57). Lithiation of 2,3-dibromothiophene 304 using -butyllithium followed by oxidative coupling with cupric chloride provided 3,3 -dibromo-2,2 -bithiophene 305 in 79% yield. Treatment of 305 with 2 equiv of -butyllithium in ether at —78 °C under nitrogen for 40 min and then adding benzenesulfonic acid thioanhydride and leaving the reaction mixture to reach room temperature afforded dithieno[3,2-A2, 3 -<7]thiophene 15a in 70% yield <2002TL1553>. [Pg.674]

Phenyliodine bis(trifluoroacetate) in combination with a Lewis acid has been shown to mediate selective oxidative cyanation of thiophenes at C-2 using TMSCN as the cyanide source <07JOC109>. Likewise, oxidative coupling of thiophenes with A-aromatic methanesulfonamides in the presence of PhI(OAc)2 in hexafluoroisopropanol (HFIP) takes place at C-2 of the thiophene, rendering for example the product 43 <07OL2553>. [Pg.101]

This concept has been extended to oligothiophenes as well. A series of oligothiophenes, containing two to six thiophene units, and entirely surrounded by bicyclooctene frameworks have been constructed using a combination of Stille coupling (see Section 3.10.2.11.2) and oxidative coupling <1996CHEC-II(2)491>. [Pg.755]

Polymerization of thiophenes by oxidative coupling has been discussed earlier <1996CHEC-II(2)491>. The generally accepted mechanism for the electropolymerization of thiophene may also be valid in the case of chemical oxidative polymerization. The steps involved are formation of a radical cation, spin-pairing of two such radical cations to form a dihydrodimer dication, loss of protons with concomitant rearomatization, and repetition of this cycle with the dimer. Couplings take place at the position of highest unpaired-electron spin density. [Pg.756]

Step 3 dithieno[2,3-b 3, 2 -l]thiophene derivatives, (I), have also been prepared by oxidative coupling using iron(III)acetylacetate (2) as illustrated in Eq. 1 and described (2). [Pg.656]

A small amount of bisthiophene was isolated when thiophene was treated with Pd(OAc), [35]. The oxidative couplings of a thiophene with thiophene, furan, or substituted arenes were achieved in poor to moderate yields using PdfOAc), in HOAc [36-38]. The oxidative couplings of thiophene or benzo[Z ]thiophene with olefins also suffer from inefficiency [39]. [Pg.256]

To summarize, electrophilic substitutions and metalations of thiophenes take place preferably at the a-positions due to the electronegativity of the sulfur atom. This is the consequence of the more effective incorporation of lone pair electrons on the sulfur into the aromatic system. In contrast, electrophilic substitution of benzo[fe]thiophenes occurs at the P-position however, the preference is not strong and substitution can result in other positions. Like thiophene, metalation and metal-halogen exchange are favored at the a-position. Also, oxidative couplings of thiophenes and benzothiophenes are not very... [Pg.294]

Oxidative coupling with formation of bithiophenes 78UK1231. Photochemical reactions of thiophenes 85HC(44,1)745. [Pg.314]


See other pages where Thiophenes oxidative coupling is mentioned: [Pg.892]    [Pg.651]    [Pg.236]    [Pg.185]    [Pg.88]    [Pg.96]    [Pg.1149]    [Pg.743]    [Pg.129]    [Pg.892]    [Pg.120]    [Pg.441]    [Pg.346]    [Pg.105]    [Pg.99]    [Pg.4173]    [Pg.30]    [Pg.54]    [Pg.473]    [Pg.4]    [Pg.21]    [Pg.41]    [Pg.45]    [Pg.892]    [Pg.509]    [Pg.529]    [Pg.186]    [Pg.474]    [Pg.171]    [Pg.37]    [Pg.39]    [Pg.229]    [Pg.338]   
See also in sourсe #XX -- [ Pg.234 ]

See also in sourсe #XX -- [ Pg.234 ]




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