| Room-temperature Negishi cross-coupling of unactivated alkyl bromides with alkyl organozinc reagents utilizing a Pd/N-heterocyclic carbene catalyst. | |
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MedLine Citation:
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PMID: 16209599 Owner: NLM Status: PubMed-not-MEDLINE |
Abstract/OtherAbstract:
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A high-yielding cross-coupling reaction of unactivated alkyl bromides possessing beta-hydrogens with alkylzinc halides utilizing a Pd/N-heterocyclic carbene (NHC) catalyst at room temperature is described. A variety of Pd sources, Pd2(dba)3, Pd(OAc)2, or PdBr2, with the commercially available ligand precursor 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (IPr.HCl) successfully coupled 1-bromo-3-phenylpropane with n-butylzinc bromide in THF/NMP. An investigation of different NHC precursors showed that the bulky 2,6-diisopropylphenyl moiety was necessary to achieve high coupling yields (75-85%). The corresponding ethyl analogue was moderately active (11%). A range of unsymmetrical NHC precursors were prepared and evaluated. The ligand precursor containing one 2,6-diisopropylphenyl and one 2,6-diethylphenyl afforded the coupling product in 47% yield, clearly suggesting a direct relationship between the steric topography created by the flanking N-substituents and catalyst activity. Under optimal conditions, a number of alkyl bromides and alkylzinc halides possessing common functional groups (amide, nitrile, ester, acetal, and alkyne) were effectively coupled (61-92%). It is noteworthy that beta-substituted alkyl bromides and alkylzinc halides successfully underwent cross-coupling. Also, under these conditions alkyl chlorides were unaffected. |
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Authors:
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Niloufar Hadei; Eric Assen B Kantchev; Christopher J O'Brien; Michael G Organ |
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Publication Detail:
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Type: Journal Article |
Journal Detail:
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Title: The Journal of organic chemistry Volume: 70 ISSN: 0022-3263 ISO Abbreviation: J. Org. Chem. Publication Date: 2005 Oct |
Date Detail:
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Created Date: 2005-10-07 Completed Date: 2006-06-28 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 2985193R Medline TA: J Org Chem Country: United States |
Other Details:
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Languages: eng Pagination: 8503-7 Citation Subset: - |
Affiliation:
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Department of Chemistry, York University, 4700 Keele Street Toronto, ON, Canada M3J 1P3. |
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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