Arene-thiophenes

Figure 16.19 Chemical structures of various arene-thiophenes andperfluoroarene - thiophenes...

Transistor activity was observed for all semiconductor films but only when applying positive biases for 31, 34 and 35 (n-channel) and negative biases for 28-30, 32 and 33 (p-channel). Ambipolar behavior was not observed in any case. For p-channel arene-thiophenes 28-30, hole mobilities vary over a very... 

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]. 

There are reports of an increasing number of palladium-assisted reactions, in some of which the palladium has a catalytic function. Thus furan and thiophene undergo facile palladium-assisted alkenylation giving 2-substituted products. Benzo[6 Jfuran and TV- acetyl-indole yield cyclization products, dibenzofurans and carbazoles respectively, in addition to alkenylated products (8UOC851). The arylation of pyrroles can be effected by treatment with palladium acetate and an arene (Scheme 86) (81CC254). 

Thermal arene exchange of tetramethylthiophene with [(/ -cymene)RuCl2]2 affords 130 (89JA8828), which on reaction with AgBE4 and excess tetramethylthiophene yields 131. The Ru—S thiophenic cluster, 132, was synthesized by reaction of 130 with (Mc3Si)2S followed by anionic metathesis and formation of the PFg salt. The coordination geometry around each ruthenium atom is pseudooctahedral. 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

Fig. 13. Bromination of arenes with BTMA Bt3 Bromination of thiophene derivatives...

Yagi S, Ohta T, Akagi N, Nakazumi H (2008) The synthesis and optical properties of bis-squarylium dyes bearing arene and thiophene spacers. Dyes Pigm 77 525-536... 

The dehalogenation of several types of polyhalogenated arenes has been studied by Hofs group [61-67]. Brominated thiophenes and bithiophenes were re-... 

Palladium chemistry involving heterocycles has its unique characteristics stemming from the heterocycles inherently different structural and electronic properties in comparison to the corresponding carbocyclic aryl compounds. One example illustrating the striking difference in reactivity between a heteroarene and a carbocyclic arene is the heteroaryl Heck reaction (vide infra, see Section 1.4). We define a heteroaryl Heck reaction as an intermolecular or an intramolecular Heck reaction occurring onto a heteroaryl recipient. Intermolecular Heck reactions of carbocyclic arenes as the recipients are rare [12a-d], whereas heterocycles including thiophenes, furans, thiazoles, oxazoles, imidazoles, pyrroles and indoles, etc. are excellent substrates. For instance, the heteroaryl Heck reaction of 2-chloro-3,6-diethylpyrazine (1) and benzoxazole occurred at the C(2) position of benzoxazole to elaborate pyrazinylbenzoxazole 2 [12e]. 

One active field of research involving the Heck reaction is asymmetric Heck reactions (AHR). The objective is to achieve enantiomerically-enriched Heck products from racemic substrates using a catalytic amount of chiral ligands, making the process more practical and economical Although intermolecular Heck reactions that occurred onto carbocyclic arenes are rare, they readily take place onto many heterocycles including thiophenes, furans, thiazoles, oxazoles,... 

Oxyiminium cations formed from iV,0-diaIkyhydroxylamines and formaldehyde are sufficiently reactive for Mannich reactions with activated arenes. Mannich reactions of oxyiminium cations with indoles (e.g. 74, equation 48) " as well as pyrroles and furans but not phenol and thiophene have been reported. 

R = OAc). Besides benzene, electron-rich arenes as well as thiophenes were successfully benzylated. 

N-, 0-, and S-heterocyclic ligands also form [Os(NH3)5 t)2-(C,C)-L ]2+ complexes [L = 2,6-lutidine, 2,6-lutidinium, pyridinium, N-methylpyridinium, and lV-methyl-4-picolinium (85, 167), NJV -dimethylimidazolium (90), pyrrole (90, 179), IV-methylpyrrole (90, 179), thiophene (90,179), furan (90,179), and 1,3-dimethyluracil (72, 73)]. On oxidation to Os(III), arene ligands are rapidly lost from the coordination sphere, or in the case of the substituted arene ligands with good a donors, rapid linkage isomerization reactions occur (Section V,D). 

Metallacyclopentadienes undergo a range of synthetically versatile reactions which proceed with extrusion of the metal atom and attendant ligands. Thus, reactions with alkenes and alkynes afford cyclohexa-1,3-dienes and arenes (Scheme 6), and thiophenes, selena-cyclopentadienes, pyrroles and cyclopentadienones (indenones, fluorenones) can be obtained by treatment with sulfur, selenium, nitroso compounds and CO, respectively. The best studied substrates for such reactions are cobaltacyclopentadienes of the type (24a), which have been converted into a wide variety of arenes, cyclohexadienes and five-membered heterocycles, many of which would be very difficult to obtain by conventional organic procedures (74TL4549, 77JOM(139)169, 80JCS(P2)1344). 

A flexible means of access to functionalized supports for solid-phase synthesis is based on metallated, cross-linked polystyrene, which reacts smoothly with a wide range of electrophiles. Cross-linked polystyrene can be lithiated directly by treatment with n-butyllithium and TMEDA in cyclohexane at 60-70 °C [1-3] to yield a product containing mainly meta- and para-Iithiated phenyl groups [4], Metallation of noncross-linked polystyrene with potassium ferf-amylate/3-(lithiomethyl)heptane has also been reported [5], The latter type of base can, unlike butyllithium/TMEDA [6], also lead to benzylic metallation [7]. The C-Iithiation of more acidic arenes or heteroar-enes, such as imidazoles [8], thiophenes [9], and furans [9], has also been performed on insoluble supports (Figure 4.1). These reactions proceed, like those in solution, with high regioselectivity. 

The arylation of support-bound arenes has mainly been performed using the Suzuki and Stille coupling reactions. Both reactions proceed smoothly with arenes and het-eroarenes such as furans, thiophenes, or pyridines. Examples of the arylation of het-eroarenes are presented in Chapter 15. 

The iodination of cross-linked polystyrene has been achieved using iodine under strongly acidic reaction conditions [55] or in the presence of thallium(III) acetate [61], but this reaction does not proceed as smoothly as the bromination. More electron-rich arenes, such as thiophenes [45,62-64], furans [46], purines [65], indoles [66], or phenols [67,68] are readily halogenated, even in the presence of oxidant-labile linkers (Figure 6.2). Polystyrene-bound thiophenes have also been iodinated by lithiation with LDA followed by treatment with iodine [64],... 

The requirement for AlCh adds some obvious limitations, but a modest number of substituted arenes have been successfully coordinated to the [FeCp]+ unit. Photoinduced arene exchange has been described43 and is particularly effective with the -r -chlorobenzene-r -cyclopentadienyliron cation without the need for Lewis acids.42 More basic (electron rich) arenes readily replace chlorobenzene, leading to FeCp cation complexes of O-phenylethyl-p-toluenesulfonate and variously substituted thiophenes.42 The charged complexes are not purified by conventional organic techniques, such as chromatography, but re-crystallization is possible. The complexes are very air and heat stable again, methods of removal of the arene from the Fe are few. The simplest is pyrolysis at >200 C.46... 

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