Thiophenes coupling reactions

Genkina et al. (1979, 1981, 1985) investigated azo coupling reactions of indoles with fused benzo and benzothiopheno rings, namely 4,5- and 6,7-benzindole, 4,5,6,7-dibenzindole (12.42), indolo[6,5]-, -[4,5]-, and -[5,4]-benzo[Z ]thiophene (12.43 to 12.45). Arenediazonium ions reacted with all these indole derivatives at the 3-position. 

The progress on S-C bond activation, which covers the reduction of a C-S bond to a C-H bond, cross coupling reaction of sulfides with main group organometaUic nucleophiles, ring opening reactions of thietanes and thiiranes, and desulfurization of thiols, sulfides, and thiophenes has already been reviewed elsewhere [6-10], and... 

The heteroaromatic stannanes undergo the normal electrophilic substitution reactions of their protic precursors, and often to an enhanced degree. They are often prepared with the aim of a subsequent Stille cross-coupling reaction, and oligothiophenes with potentially useful optical and electron properties have been prepared by coupling between stannyl- and bromo-thiophenes, for example, Equation (63).204... 

The coupling reaction of acetylenic carbinols was also extended to the thiophene series (80). The diacetylenic glycols were of particular interest, since they provide convenient synthetic routes to bifunctional compounds difficult to prepare by other means. The coupling reaction, which took place, could be represented as follows ... 

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. 

A new class of photochromic diarylethenes containing thieno[3,2-b] thiophenes, dithieno[3,2-b 2, 3 -d]thiophene (08CC5203), and dithieno [3,2-fc 2, 3 -d]pyrroles (09CEJ10005) with photoswitchable luminescence properties were synthesized by Suzuki cross-coupling reactions (Scheme 48). 

The 2-bromo-4,6-dihydrothieno[3,4-, ]thiophene-5,5-dioxide 211 was used in the synthesis of 5-(5,5-dioxo-5,6-dihydro-477-5A -thieno[3,4-, ]thiophen-2-yl)-3,3"-dipentyl[2,2 5, 2"]terthiophene 213 by Suzuki cross-coupling reaction with 5-bromo-3,3"-dipentyl-[2,2 5, 2"]terthiophene 212 (Scheme 20) <1998S1372>. 

The coupling reaction of Fischer carbene complexes, 96, with 3-alkynyl-2-thiophene carboxaldehyde leads to the formation of thieno[2,3-c]pyranones (Scheme 25) <2001TL777, 2002JOC4177>. This reaction is applicable to the oxygenated derivatives. 

As we have already seen in several examples, the electron withdrawing nature of the nitrogen atoms in heterocyclic systems leads to a marked increase in their ability to participate in cross-coupling reactions. The triazolo[l,5-a]quinazoline system in 8.23. is a nice example, since not only the 5-chloro, but also its 5-tosyloxy derivative was shown to couple readily with 2-tributylstannyl-thiophene in 78% and 91% yield respectively.32 Interestingly, in case of the chloro derivative the addition of copper... 

Cross-coupling reactions between organoboranes and heteroaryl halides are effectively catalyzed by Pd(0) in the presence of a base. Couplings in simple pyrimidines are illustrated by the reaction between 2-chloropyrimidine and 2- or 3-thiophene- and selenophene-boronic acids which give the corresponding 2-substituted pyrimidines (921) (Scheme 72). In 2,4-dichloro- or 2,4-dibromo-pyrimidine it is the 4-halo substituent which is the more reactive. 

Much work has been directed towards the synthesis of thiophene oligomers and polymers. This is due to the current interest in research on conducting polymers and molecular electronics (92CRV711). Two main approaches have been used for making such polymers (i) chemical (e.g. FeCl3) or electrochemical oxidation of monomeric thiophenes and (ii) transition metal-catalyzed cross-coupling reactions. 

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