Pyrrole cross-coupling reactions

The bromine atoms in 2,5-dibromo-l,3,4-thiadiazole 54 undergo a palladium-catalyzed Stille reaction with the organostannyl derivative 55 (Equation 7) <1998CEJ2211>. The thiadiazole 54 was co-polymerized with diethynyl benzene 56 (Equation 8) and diethynyl pyrrole in a Sonogashira cross-coupling reaction <2005MM4687>. 

TMS group and the Suzuki cross-coupling reaction is again repeated. This sequential process allows for the introduction of different aromatic groups at positions 3 and 4 of the pyrrole system. The synthesis of the Furstner intermediate (6) is completed by removal of the sulfonamide group. 

This route involves the conversion of a 3,4-diiodopyrrole (139) to the corresponding 3,4-diboronate ester (140) followed by a bis Suzuki cross-coupling reaction with a bromoquinoline, which generates the halitulin core (141). This pyrrole (141) is then alkylated with a tosylated cycloazadecane to generate a pentasubstituted pyrrole (143), which is converted to halitulin by debenzylation under hydrogenolysis conditions. 

The Pd-catalyzed cross coupling reaction of 3-stannylated pyrroles is also known. Muchowski has thus prepared and utilized 96 to effect Stille couplings leading to 97 [59]. 

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 4- and 6-positions of pyrrolo[2,3-3]pyridines can be substituted via palladium-catalyzed cross-coupling reactions with the 4- or 6-halo-substituted derivatives (Scheme 3) <2001SL609>. Nucleophilic displacement of the 4-substituent of 6-chloro-4-nitro- and 4,6-dichloro-pyrrolo[2,3-/ ]pyridines takes place with phenols. Protection of the pyrrole nitrogen with a /3-trimethylsilylethoxymethyl (SEM) group affords good yields of the aryl ethers (Equation 3) <2006TL2069>. 

A cross-coupling reaction (Negishi coupling) between A -SEM-pyrrol-2-yl-zinc chloride 618 and the appropriate dibromo derivative catalyzed by a Ni catalyst leads to 2-[4-(l//-pyrrol-2-yl)phenyl]-l//-pyrroles 619 (Scheme 125) <1997CM2876>. The SEM-protecting group can be easily removed by reaction with BU4NF. 

Methoxy-5-(177-pyrrol-2-yl)-2-thienyl]-177-pyrrole 621 was also prepared by a cross-coupling reaction, Stille reaction in this case, between A -SEM-2-(trimethylstannyl)-l/7-pyrrole 620 and 2,5-dibromo-3-methoxythiophene in the presence of a Pd catalyst, followed by nitrogen deprotection (Scheme 126) <1997CM2876>. If Negishi coupling is applied, the main reaction product is, in this case, A -SEM-2,2 -dipyrrole, and the desired compound can be isolated only in trace amount. 

The Suzuki cross-coupling reaction between 1,2,5-trisubstituted pyrrole halides 1443 and 2-A -(/-butoxycarbonyl)-aminophenyl boronic acid 1444 performed with benzyl[bis(triphenylphosphine)]palladium(ll) chloride (PdBnCl(PPh3)2)... 

From a synthetic point of view, lamellarins are rather complex molecules. In the literature, there are described several approaches, which fall into two main synthetic categories (i) by pyrrole formation as the key step of the synthesis and (ii) by transformation of a pre-existent pyrrole derivative through cross-coupling reactions. Although and due to the structural... 

Stille and Suzuki cross-coupling reactions failed when the authors tried to obtain the mono-arylated pyrrole under different conditions. As a consequence, these types of coupling reactions would not seem to be useful in providing access to differentially di-arylated pyrrole systems... 

Palladium-catalysed cross-coupling reactions involving pyrroles Banwell, M. G., Goodwin, T. E., Ng, S., Smith, J. A. and Wong, D. J., Eur. J. 

The formation of borylated heterocyclic compounds has attracted much interest with regard to their use as starting materials for cross-coupling reactions, the possible formation of interesting macrocyclic species, and their applications in optoelectronic materials. Several synthetic routes are available for the borylation of the five-membered heterocycles thiophene, furan, pyrrole, and related compounds (101-103 ... 

The most important palladium-catalyzed processes include Heck vinylation of halides and sulfonates and various cross-coupling reactions in which a nucleophilic intermediate (stannane, organo-zinc halide or boronic acid) is coupled with an electrophile (halide or sulfonate). These coupling reactions are usually restricted to arylation and vinylation because of the tendency of alkylpalladium species to undergo elimination. The pyrrole and indole rings can participate in cross-coupling as either the nucleophilic or electrophilic component. 

In terms of C-3 substitution reactions, the regioscleclive borylation of 1-triisopropylsilyl-pyrrole (77) was achieved providing a valuable reagent for cross-coupling reactions <01OL2831>. Thus, reaction of 77 with the rhodium precatalyst shown in the presence of pinacolborane affords the C-3 substituted derivative 78. 

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