期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 19, 期 5, 页码 1658-1665出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201203331
关键词
cross-coupling; dendrimers; NHC ligands; nickel catalysts; oligothiophenes
资金
- JSPS, Japan
- Nagase Science Promotion Foundation
- Japan Science Society
- Grants-in-Aid for Scientific Research [22350042] Funding Source: KAKEN
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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