Concise Synthesis of Well‐Defined Linear and Branched Oligothiophenes with Nickel‐Catalyzed Regiocontrolled Cross‐Coupling of 3‐Substituted Thiophenes by Catalytically Generated Magnesium Amide |
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Authors: | Shota Tanaka Daiki Tanaka Go Tatsuta Kohei Murakami Shunsuke Tamba Dr Atsushi Sugie Prof Dr Atsunori Mori |
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Institution: | Department of Chemical Science and Engineering, Kobe University, 1‐1 Rokkodai, Nada, Kobe 657‐8501 (Japan), Fax: (+81)?78‐803‐6181 |
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Abstract: | 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. |
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Keywords: | cross‐coupling dendrimers NHC ligands nickel catalysts oligothiophenes |
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