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Structure-Reactivity Relationships of Lithium Amides: LiHMDS-Mediated Enolizations of Hindered Aryl Ketones and LiTMP-Mediated Ortholithiations
Başlık:
Structure-Reactivity Relationships of Lithium Amides: LiHMDS-Mediated Enolizations of Hindered Aryl Ketones and LiTMP-Mediated Ortholithiations
Yazar:
Mack, Kyle Anthony, author. (orcid)0000-0002-4986-4040
ISBN:
9780438025660
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (195 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Advisors: David B. Collum Committee members: Geoffrey W. Coates; Brett P. Fors.
Özet:
Enolizations of highly substituted acyclic ketones used in the syntheses of tetrasubstituted olefin-based anticancer agents are described. Lithium hexamethyldisilazide (LiHMDS)-mediated enolizations are moderately Z-selective in neat tetrahydrofuran (THF) and E-selective in 2.0 M THF/hexane. The results of NMR spectroscopy show the resulting enolates to be statistically distributed ensembles of E,E-, E,Z-, and Z,Z-enolate dimers with subunits that reflect the selectivities. The results of rate studies trace the preference for E and Z isomers to tetrasolvated- and pentasolvated-monomer-based transition structures, respectively. Enolization using LiHMDS in N,N-dimethylethylamine or triethylamine in toluene affords a 65:1 mixture of LiHMDS?lithium enolate mixed dimers containing E and Z isomers, respectively. Spectroscopic studies show that condition-dependent complexation of ketone to LiHMDS occurs in trialkylamine/toluene. Rate data attribute the high selectivity exclusively to monosolvated-dimer-based transition structures.
Rate and mechanistic studies of ortholithiations by lithium 2,2,6,6-tetramethylpiperidine focus on four arenes: 1,4-bis(trifluoromethyl)benzene, 1,3-bis(trifluoromethyl)benzene, 1,3-dimethoxybenzene, and 4,4-dimethyl-2-phenyl-2-oxazoline. Metalations occur via substrate-dependent combinations of monosolvated monomer, disolvated monomer, and tetrasolvated dimer (triple ions). Density functional theory computational studies augment the experimental data. We discuss the challenges presented by shifting dimer--monomer proportions in determining the observable reaction orders and our mathematical treatment of such shifting in reactant structure.
Notlar:
School code: 0058
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(678258.1) | 678258-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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