| Kinetic studies on the stability and reactivity of beta-amino alkylzinc iodides derived from amino acids. | |
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MedLine Citation:
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PMID: 18855456 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Beta-amino alkylzinc iodides are intrinsically unstable toward beta-elimination and protonation. The aim of this study was to determine the rates of these processes and also to understand how the reactivity of a range of beta-amino alkylzinc iodides in Negishi cross-coupling reactions is influenced by the presence of functional groups within the zinc reagent. Decomposition of beta-benzamido alkylzinc iodides occurs by protonation, and the first-order rate constant for the self-protonation of the carbon-zinc bond in reagent 4b was determined to be 5.2 x 10(-6) s(-1) (at 291 K). In contrast, the carbamate derivative 2 decomposes by a first-order elimination process. The homologous reagent 3, derived from glutamic acid, decomposes more quickly by beta-elimination, with a first-order rate constant of 24 x 10(-6) s(-1) (at 291 K). Reagents 23 and 25, in which the Boc group has been replaced with a trifluoroacetyl group, are more stable toward beta-elimination than the corresponding reagents 2 and 3, a striking outcome given that the trifluoroacetamido group is a better leaving group. Moreover, this replacement also changes the mechanism of the elimination to a second order process. Pseudo-second-order rate constants for the Negishi cross-coupling of reagents 2, 3, 23, and 25 with iodobenzene have been determined, revealing the higher reactivity of the glutamic acid-derived reagents 3 and 25. The main factor influencing reactivity, therefore, is determined to be the proximity of the ester group, rather than the nature of the nitrogen protecting group. Finally, beta-amino alkylzinc iodides 46-48 containing Weinreb amides have been prepared, rate constants for their decomposition through elimination determined, and their synthetic potential for the preparation of beta-amino ketones established. |
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Authors:
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Ian Rilatt; Richard F W Jackson |
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Publication Detail:
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Type: Journal Article; Research Support, Non-U.S. Gov't Date: 2008-10-15 |
Journal Detail:
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Title: The Journal of organic chemistry Volume: 73 ISSN: 1520-6904 ISO Abbreviation: J. Org. Chem. Publication Date: 2008 Nov |
Date Detail:
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Created Date: 2008-11-14 Completed Date: 2009-01-09 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: 8694-704 Citation Subset: IM |
Affiliation:
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Department of Chemistry, The University of Sheffield, Dainton Building, Sheffield S3 7HF, United Kingdom. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Amines
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chemistry* Amino Acids / chemistry* Benzamides / chemistry Carboxylic Acids / chemistry Indicators and Reagents / chemistry Iodine / chemistry* Kinetics Organometallic Compounds / chemistry* Zinc / chemistry* |
| Chemical | |
Reg. No./Substance:
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0/Amines; 0/Amino Acids; 0/Benzamides; 0/Carboxylic Acids; 0/Indicators and Reagents; 0/Organometallic Compounds; 7440-66-6/Zinc; 7553-56-2/Iodine |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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