2,2 -Bithiophene reactions

In 2000, these authors also developed a very efficient diphosphine-bithiophene ligand, tetraMe-BITIOP, which is depicted in Scheme 8.29. The ruthenium complex of this electron-rich diphosphine was used as the catalyst in asymmetric hydrogenation reactions of prostereogenic carbonyl functions of a-... 

Table 9 Properties of T-T absorption bands and reaction rates of bithiophene derivatives in triplet excited state...

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>. 

Dipolar cycloaddition of 2,4-(trimethylsilyl)- and 2,4-(trimethylgermyl)-substituted thiophene-1,1-dioxides as well as silylated 2,2 -bithiophene-1,1-dioxides was investigated. It was shown that only the C(4)=C(5) double bond of 2,4-disubstituted thiophene-1,1-dioxides interacts with acetonitrile oxide to give thienoisoxazoline dioxides. Bithiophene derivatives were inactive or their reaction with nitrile oxide was accompanied by desilylation. Cycloaddition of benzonitrile oxide with all mentioned sulfones did not occur. The molecular structure of 3a-methyl-5.6a-bis(trimethylgermyl)-3a,6a-dihydrothieno 2.3-c/ isoxazole 4,4-dioxide was established by X-ray diffraction (263). ... 

Advantage has been taken of the aforementioned observations in the synthesis of a terthiophene natural product, arctic acid (147) [123]. Pd-catalyzed carbonylation of bromobisthiophene 25, obtained from the Kumada coupling of 2-thienylmagnesium bromide and 2,5-dibromothiophene, gave bithiophene ester 144, which was converted to iodide 145 by reaction with iodine and yellow mercuric oxide. Subsequent propynylation of 145 was then realized using the Sonogashira reaction with prop-l-yne to give bisthienyl alkyne 146, which was subsequently hydrolyzed to 5 -(l-propynyl)-2,2 -bithienyl-5-carboxylic acid (147), a natural product isolated from the root of Arctium lappa. 

Studies by Heinze etal. on donor-substituted thiophenes or pyrroles [33] such as methylthio (= methylsulfonyl) or methoxy-substituted derivatives provide further clear evidence for this reaction pathway. They found, for instance, that 3-methylthiothiophene or 3-methoxythio-phene (2) undergo a fast coupling reaction. However, deposition processes or insoluble film formation could not be detected in usual experiments with these compounds, even at high concentrations. Similarly, the corresponding 3,3 -disubstituted bithiophenes (2a) do not polymerize, but the anodic oxidation of 4,4 -disubstituted bithiophenes (2c) produces excellent yields of conducting polymers. 

Therefore, the reactivity of these cationic species, similar to that of all other 3,3 substituted bithiophenes or bipyrroles, is low, probably resulting in a rate constant for the dimerization of < 10 M s [33d]. The tetrameric products of the subsequent coupling are even more stable than the dimers, which means that the polymerization process stops at this level, or becomes very slow. This reaction pattern is shown in Fig. 2, where the resulting species of... 

A stirred solution of 2,2 -bithiophene (60.24 mmol) dissolved in 150 ml THF was treated with n-butyllithium (2.5M in hexanes 50.0 mmol) dropwise at -78°C and then warmed to ambient temperature over 2 hours. The mixture was then treated with 6-bromohexyloxy-t-butyl-dimethylsilane (50.0 mmol) and stirred overnight at ambient temperature. The reaction was then quenched with aqueous NH4CI and extracted three times with 70 ml ethyl acetate. Combined extracts were washed with water, brine, dried over MgS04, and concentrated. The residue was purified by... 

The copper catalyzed oxidative dimerisation of arylboronic acids was also used for the preparation of symmetrical bithiophene derivatives. 2-Formylhiophene-3-boronic acid and 5-boronic acid were both dimerised successfully giving the appropriate dithiophenes in 35% and 41% yield (6.98.). The optimised coupling conditions included running the reactions in DMF in the presence of 50 mol% copper(II) acetate.130... 

The use of methyltriphenylphosphonium bromide and MeSOCH2 on 5-bromo-2-thienyl-thiophene-2-carbaldehyde (128) furnished the corresponding olefin 133. The reaction with propyne in this case furnished a natural bithiophene 134 isolated from Tagetes minuta (86G747). 

The photochemical coupling between methyl 5-iodothiophene-2-car-boxylate (119) and 2-chlorothiophene gave the corresponding bithiophene 140. Also, in this case the reaction with propyne gave a naturally occurring bithiophene 142 isolated from Arctium lappa (89JPP(A)(47)191). 

The reaction of 5,5 -bis(pentaethyldisilanyl)-2,2 -bithiophene was chosen as a model compounds of poly[(tetraethyldisilanylene)bis(2,5-thie-nylene)]. After 77 h irradiation in benzene, they obtained 5-(pentaethyldi-silanyl)-2,2 -bithiophene (23%) and triethylphenylsilane (46%). The corresponding permethyl derivative was found to be photochemically inert. The inactivity of permethyl derivative is similar to the low photosensitivity of the permethyl polymer. 

The solvent-free, microwave-assisted coupling of thienyl boronic acids and esters with thienyl bromides, using aluminum oxide as the solid support, served to rapidly check the reaction trends on changing times, temperature, catalyst, and base and easily optimize the experimental conditions to obtain the desired product in fair amounts. This procedure offers a novel, general, and very rapid route to the preparation of soluble thiophene oligomers. Quaterthiophene 265 was obtained in 6 min by reaction of 2-bromo-2,2 -bithiophene with bis(pinacolato)diborane(4) in 65% yield, whereas dithiophene 266 was obtained with 70% yield. The synthesis of new chiral 2,2 -bithiophenes also was reported. The detailed... 

The reactions of isatin and thiophene or 2,2 -bithiophene proceed similarly to those of indoles. However, in these cases mixtures of oligomeric products were obtained448. This reaction has been applied to the synthesis of electrically conducting polymers449. 

The hexabutylditin-mediated synthesis of 5,5 -diaryl-2,2 -bithiophenes through a homocoupling reaction has been described (Equation 45) <2006TL795>. 

Reaction of 2,3-dibro o-1.4-diketone with 2 molar equiv of thioamide affords bithiophene 198 (Equation 6) <2002CL896>. 

Another mechanistic possibility is the attack of the thiophene cation radical (420) upon a neutral thiophene monomer (419) to form a cation-radical dimer (421) [247]. The oxidation and loss of two protons leads to formation of the neutral dimer (422). Once again, rapid oxidation of the dimer occurs upon its formation due to its close proximity to the electrode surface and its lower oxidation potential. The cation-radical dimer (423) which is formed then reacts with another monomer molecule in a similar series of steps to produce the trimer 425. A kinetic study of the electrochemical polymerization of thiophene and 3-alkylthiophenes led to the proposal of this mechanism (Fig. 61) [247]. The rate-determining step in this series of reactions is the oxidation of the thiophene monomer. The reaction is first order in monomer concentration. The addition of small amounts of 2,2 -bithiophene or 2,2 5, 2"-terthiophene to the reaction resulted in a significant increase in the rate of polymerization and in a lowering of the applied potential necessary for the polymerization reaction. In this case the reaction was 0.5 order in the concentration of the additive. 

Halogen-substituted thiophenium ions have low stability and can be observed by NMR only at temperatures below -30 °C (86MRC699). Disproportionation of the 2,5-dibromo-2H-thiophenium ion with formation of 5-bromo- and 3,5-dibromo-2H-thiophenium ions was observed on increasing the temperature from —50 to —10 °C (86MRC699). For chlorothiophenium ions, the disproportionation could not be observed so distinctly. Note that 2,4-dichloro-2H-thiophenium ion (5) is stable at room temperature and is the main transformation product of the less stable 2,5-dichloro-2H-thiophenium ion (2j). The latter fact was used for the preparation of difficultly available 2,4-dichlorothiophene (6) from the 2,5-isomer 3,5,4 -trichloro-2,2 -bithiophene (7) was isolated as a byproduct resulted, probably, from the reaction of ion 5 with dichloride 6 (Scheme 7) (90G365). 

The interaction of 2,4-dichlorothiophene (6) with 3,5-dichloro-2H-thiophenium ion (5) to give bithiophene 7 is an electrophilic substitution in which cation 5 is an electrophile. Similarly, the add-induced oligomerization of five-membered heteroaromatics is a resinification. The structure of 3,4-dimethylpyrrole dimer formed in 6N HCl (68JCS(C) 2526) shows that the oligomerization may proceed (Scheme 11) through a 2H-pyrrolium ion, reaction 2 in Scheme 2. 

This macrocycle was first reported by Merz and Neidlein in 1993. It was isolated in 2.9% yield as a trimeric by-product from the reductive McMurry-type self-coupling of 2,5-diformyl bithiophene 7.89 (Scheme 7.7.8), a reaction that was originally intended to produce the tetrathiaporphycenogen 7.91 (see Chapter 3). ... 

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