Concise Synthesis of Well-Defined Linear and Branched Oligothiophenes with Nickel-Catalyzed Regiocontrolled Cross-Coupling of 3-Substituted Thiophenes by Catalytically Generated Magnesium Amide

The synthesis of linear and branched oligothiophenes of well‐defined structures is performed with regioselective deprotonation of 3‐substituted thiophenes and nickel‐catalyzed cross‐coupling of the thus formed metalated species with a bromothiophene. The reaction of 3‐hexylthiophene with EtMgCl and...

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Bibliographic Details
Published in:Chemistry : a European journal 2013-01, Vol.19 (5), p.1658-1665
Main Authors: Tanaka, Shota, Tanaka, Daiki, Tatsuta, Go, Murakami, Kohei, Tamba, Shunsuke, Sugie, Atsushi, Mori, Atsunori
Format: Article
Language:English
Subjects:
Amides
Branched
Chemistry
Cross coupling
Dendrimers
Magnesium
NHC ligands
Nickel
nickel catalysts
oligothiophenes
Synthesis
Thiophenes
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Summary:The synthesis of linear and branched oligothiophenes of well‐defined structures is performed with regioselective deprotonation of 3‐substituted thiophenes and nickel‐catalyzed cross‐coupling of the thus formed metalated species with a bromothiophene. The reaction of 3‐hexylthiophene with EtMgCl and 2,2,6,6‐tetramethylpiperidine (TMP‐H, 10 mol %) induces the metalation selectively at the 5‐position by use of the catalytically generated hindered magnesium amide (TMPMgCl) and the subsequent reaction of a 2‐halo‐3‐hexylthiophene (bromide or chloride) in the presence of a nickel catalyst affords a head‐to‐tail (HT)‐type dimer. By repeating the same sequence, the linear oligothiophene up to a 4‐mer is synthesized in good yield. The reaction of 3‐hexylthiophene with 2,3‐dibromothiophene also takes place to afford a branched oligothiophene 3‐mer in quantitative yield. The obtained 3‐mer is also metalated at the sterically less‐hindered position in a regioselective manner furnishing a 7‐mer in >99 % yield after a further coupling reaction with 2,3‐dibromothiophene. These dendrimers react with several multifunctionalized organic electrophiles, leading to a variety of branched oligothiophenes. Dendrimers: A single‐step per extension protocol allows stepwise formation of the thiophene–thiophene bond, with which linear and branched oligothiophenes are synthesized in a remarkably concise manner (see scheme).
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201203331