[3.3] Sigmatropy within 1-vinyl-2-alkenyl-7,7-dimethyl-exo-norbornan-2-ols. The first atropselective oxyanionic Cope rearrangement

Paquette, Leo A.; Pegg, Neil; Toops, Dana S.; Maynard, George D.; Rogers, Robin D.

doi:10.1021/ja00157a043

Cited by 60 publications

(19 citation statements)

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“…There are numerous accounts of alkalimetal amides being used to achieve alkali-metal/hydrogen exchange, and the use of alkali-metal amides (in particular those of lithium) has been well reviewed. [8,[12][13][14][15] More specifically, the amides have been used recently in certain transformations such as the generation of enolates, [16][17][18][19][20][21][22][23][24][25] condensation and ring-formation processes, [26][27][28] directed ortho-metalations (DoM), [29][30][31][32][33][34][35][36][37][38][39] rearrangement and isomerization processes, [40][41][42][43][44] and in Wittig reactions. [45][46][47][48] From a structural perspective, the chemistry of the alkali metal amides has been the focus of a great deal of attention, both in solution and in the solid state.…”

Section: Introductionmentioning

confidence: 99%

A Structural and Computational Study of Synthetically Important Alkali‐Metal/Tetramethylpiperidide (TMP) Amine Solvates

Armstrong

Graham

Kennedy

et al. 2008

Chemistry A European J

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Two heavy alkali-metal salts of the sterically demanding amine, 2,2,6,6-tetramethylpiperidine (TMPH), have been prepared using different methodologies. Complex 1, [((tmeda)Na(tmp))2] (TMEDA=N,N, N',N'-tetramethylethylenediamine), can be synthesized by a deprotonative route. This is achieved by reacting butylsodium with TMPH in the presence of excess TMEDA in hexane. The potassium congener [((tmeda)K(tmp))2] (2), can be prepared by treating KTMP (made using a metathesis reaction between LiTMP and potassium tert-butoxide) with an excess of TMEDA in hexane. In the solid state, 1 and 2 are essentially isostructural. They are discretely dimeric and their framework consists of a four-membered M-N-M-N ring (M=Na or K, N=TMP). Due to the high steric demand of the TMP ligand, the TMEDA molecules bind to the metal centers in an asymmetric manner. In 2, each of the coordination spheres of the metals is completed by an agostic K...CH3(TMP) interaction. DFT calculations at the B3 LYP/6-311G** level give an insight into why 1 and 2 adopt dramatically different structures from their previously reported, "open-dimeric", lithium counterpart. The theoretical work also focuses on the TMEDA-free parent amide complexes and reveals that the energy difference for the formation of [(M(tmp))x] (in which, M=Li or Na, x=3 or 4; and M=K, x=2, 3 or 4) are small.

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Section: Introductionmentioning

confidence: 99%

A Structural and Computational Study of Synthetically Important Alkali‐Metal/Tetramethylpiperidide (TMP) Amine Solvates

Armstrong

Graham

Kennedy

et al. 2008

Chemistry A European J

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“…The isomeric ketone nature of this product was immediately recognized on the basis of the infrared and mass spectra. Its detailed stereochemistry, anticipated on the basis of the adoption of an endo-chair transition state [13] was deduced on the strength of its 1 Hand 13 C-NMR features and selected NOE experiments. Attention is called to the fact that the 21 Ǟ 22 rearrangement did not occur at a useful rate until the reaction temperature reached ca.…”

Section: Evaluation Of the Oxy-anionic Cope Rearrangements ؊ The Acycmentioning

confidence: 99%

From Carbohydrates to the Discovery of Pronounced Heteroatomic Effects on Anionically Accelerated [3,3]-Sigmatropic Rearrangements

et al. 2000

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The (Z)-(iodovinyl)oxetane 12 was prepared from d-glucose and the acyclic analog 18 was obtained from d-mannitol. Following the generation of their lithium derivatives by halogen−metal exchange, coupling to the enantiopure vinylsubstituted norbornanones 20, 23, and 29 proceeded exclusively via endo attack to deliver the targeted exo-carbinols. The anionic oxy-Cope rearrangements of 21 and 24 were seen to differ appreciably in rate. While the sulfur derivative 24 experiences [3,3] sigmatropy with a half-life of less than a minute at −78°C, its oxygen analogue 21 proved unreactive below −20°C under entirely comparable conditions. This phenomenon is critically examined in a synthetic context in-

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“…In the case of 1, exposure to vinyllithium reagents results in wholesale (>95%) enolization. 4 For 2, direct 1,2-addition is readily accommodated without this complication. 5 On the basis of the preceding considerations, one can derive the expectation that the properties of an a-oxygen atom should invariably promote enolization of the substituted ketone away from the a' site (see A).…”

Section: Background Developmentsmentioning

confidence: 99%

The Need for an Incisive Analysis of the Regioselectivity Associated with the Deprotonation of α-Alkoxy and α-Acyloxy Ketones

Paquette¹,

O’Neil²,

Guillo³

et al. 1999

Synlett

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A summary of informative examples involving the regioselective deprotonation of a-oxygenated ketones has been compiled from the literature and augmented by new findings from the authors' laboratory. The text provides a brief discussion of the complexity of the matter. The data are tabulated with regard to enolization both away from and toward the oxygen substituent, with subsequent capture at oxygen or carbon. The possible role of steric, electronic, and conformational factors is addressed in a manner that points up the need for a more detailed understanding of these enolizations as a general process.

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[3.3] Sigmatropy within 1-vinyl-2-alkenyl-7,7-dimethyl-exo-norbornan-2-ols. The first atropselective oxyanionic Cope rearrangement

Cited by 60 publications

References 0 publications

A Structural and Computational Study of Synthetically Important Alkali‐Metal/Tetramethylpiperidide (TMP) Amine Solvates

A Structural and Computational Study of Synthetically Important Alkali‐Metal/Tetramethylpiperidide (TMP) Amine Solvates

From Carbohydrates to the Discovery of Pronounced Heteroatomic Effects on Anionically Accelerated [3,3]-Sigmatropic Rearrangements

The Need for an Incisive Analysis of the Regioselectivity Associated with the Deprotonation of α-Alkoxy and α-Acyloxy Ketones

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