Stereoselectivity in the Reactions of Nitrosopiperidine Carbanions. Steric <i>vs</i>. Stereoelectronic Control

Fraser, Robert R.; Grindley, T. Bruce; Passannanti, Salvatore

doi:10.1139/v75-352

Cited by 39 publications

(6 citation statements)

References 17 publications

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“…Hence other factors must also be involved in the shieldings. I11 the N-nitroso derivative of piperidine where the dihedral angle between the N-N and the a C-H bonds is Oo, a value of A6(sy/i-anti) = -11.0 ppm was observed in 13Cnir whereas in 'Hmr this difference was only 0.03 p p~n (9). In this type of compound both the steric cnnipression model (9) and the electric field effect (20) have been invoked to explain the 13C shifts.…”

Section: The Results Given Inmentioning

confidence: 99%

Conformational analysis of ketoximes by the application of carbon-13 nuclear magnetic resonance spectroscopy

Geneste¹,

Durand²,

Kamenka³

et al. 1978

Can. J. Chem.

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DPparte~?lerrt cle Chimie, Urriversite' d e Sherbrooke, Sherbrooke (Que'.) C a~l a t f a JIK 2RI Received July 25, 19772 PATRICK GENESTE, ROBERT DURAND, JEAN-MARC KAMENKA, HELMUT BEIERBECK, ROBERT MARTINO, and JOHN K. SAUNDERS. Can. J. Chern. 56, 1940Chern. 56, (1978.The carbon-13 chemical shifts for a number of relatively rigid ketoximes are presented. It is shown that the chemical shift difference, A6 (sj~rr-onri), for the carbons a to the oxime carbon depends on the dihedral angle between the C=N and C. -H bonds. This stereochernical dependence is then used to determine the preferred conforn~ation of substituted cyclohexanone oximes.PATRICK GENESTE, ROBERT DURAND, JEAN-MARC KAMENKA, HELMUT BEIERBECK, ROBERT MARTINO et JOHN K. SAUNDERS. Can. J. Chen~. 56, 1940Chen~. 56, (1978.O n rapporte les diplacements chiniiques du carbone-13 d'un certain nombre de cetoximes relativement rigides. O n dinlontre que la difference des deplacements chimiques, A6(sj~rr-orrli), pour les carbones en a du carbone de I'oxirne depend de I'angle diedre entre les liens C=N et C,-H.O n utilise ensuite cette correlation sterCochimique pour determiner la conformation privilegie des oxinles de cyclohexanone substitues.[Traduit par 1e journal]Currently, carbon-13 nuclear magnetic resonance spectroscopy (13Cmr) is an infornlative and important technique for conformational analysis. The shielding parameters have been shown to be very sensitive to environment (I) such that relatively small conformational changes lead to significant chemical shift variations. During a study of the reactivity of ketones and ketoximes, it was necessary to have increased knowledge of their confor~liations i l l solution. From earlier reports (2, 3), it appeared that 13Cmr may furnish such information since AS(syna l~t i ) values for the carbons a to the oxime carbon are significant and hence we undertook a study of the 13Cmr chemical shifts of a number of relatively rigid ketoximes. In this paper we present the results of this study and their subsequent use in the conformational analysis of substituted cyclohexanone oximes.signments for the remaining conlpounds were made with the aid of single frequency off-resona~lce decoupled (sford) spectra, from the chemical shifts f o r the corresponding ketones (4), a n d the observation (2,3) that for carbons a to the C=N bond, the carbon sy17 to the OH group is shielded relative to the a l~t i position. Also, for oximes whose corresponding ketones do not have two-fold symmetry, disting~~ishable isomers exist, which were generally present in unequal amounts. For compound 2, carbons I, 2,4, 6, 7 (the quaternary carbon), and 8 (the CH, carbons) were readily assigned from the sford spectrunl. T h e protons on carbon 2 have a chemical shift difference of 1 ppm (5) and thus this carbon appeared in t h e sford spectrum a s the X part of an ABX system, whereas the other methylenes appeared as the normal triplets. The remaining resonances were assigned t o carbons 3 and 5 o n the basis of the different shifts in- Resultsduc...

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Section: The Results Given Inmentioning

confidence: 99%

Conformational analysis of ketoximes by the application of carbon-13 nuclear magnetic resonance spectroscopy

Geneste¹,

Durand²,

Kamenka³

et al. 1978

Can. J. Chem.

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“…48 Extreme care to minimize exposure is necessary when using any N-nitrosamine reagents. Based on work conducted by Fraser, 49 Seebach showed that 4-phenylpiperidinederived amide 85 undergoes lithiation and alkylation at the equatorial position to give 2,4-cis-piperidine 86 (Scheme 16B). 50 The stereochemical disparity in the alkylation of the N-nitroso and N-acyl examples suggested the organolithium intermediates were congurationally stable.…”

Section: Generation Structure and Reactivitymentioning

confidence: 99%

Generation, structure and reactivity of tertiary organolithium reagents

Perry¹,

Rychnovsky

2015

Nat. Prod. Rep.

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Tertiary alkyllithium reagents are very useful intermediates in synthesis. Alkyllithium reagents with adjacent heteroatoms may be formed stereoselectively or may react stereoselectively, and have been used in the synthesis of alkaloids, C-glycosides and spirocycles. An overview of the generation, reactivity and stereochemistry of tertiary alkyllithium reagents will be presented, as well as examples of their use in organic synthesis. The discussion will be focused on a conceptual understanding of the generation and reactivity of these intermediates. The reactions described herein generate fully substituted carbon atoms, and the forces driving stereoselectivity will be discussed in detail. Where appropriate, computational results will be introduced to provide a better understanding for the structure and reactivity of tertiary alkyllithium reagents.

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“…Thus it seems very likely that lithium bromide and lithium methoxide are present as impurities in the commercial samples of methyllithium used for these reactions. A recent paper has described problems arising in organic syntheses from the presence of lithium bromide in solutions of methyllithium supplied by the Ventron Corporation (10). reaction with water prior to addition of the Et30BF4.…”

Section: The Reaction Of Phzgemn(co)4come With Melimentioning

confidence: 99%

The reactivity of cyclic germoxycarbene complexes of manganese and rhenium towards nucleophiles

Webb¹,

Graham²

1976

Can. J. Chem.

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. Can. J. Chem. 54, 2557Chem. 54, (1976. Several acylate salts and noncyclic carbene complexes of manganese and rhenium, containing organogermanium ligands, have been prepared via the reactions of the cyclic germoxycarbene complexes of empirical formula Ph2GeM(C0)4COMe (M = Mn, Re) with the nucleophiles methyllithium or methoxide ion. In each case the observed product could be rationalized in terms of nucleophilic attack at germanium. Treatment of Ph2GeRe(C0)4COMe with methyllithium, followed by ethylation with aqueous Et30BF4, afforded ~is-Ph~MeGeRe(C0)~C-(0Et)Me. The manganese analog of this product could be obtained if excess methyllithium were used in the first step. The use of a deficit of methyllithium, however, followed by ethylation, yielded ci~-Ph~FGeMn(C0)~C(0Et)Me. Solution infrared spectra have indicated that lithium methoxide and lithium bromide impurities in the methyllithium are involved in this reaction. The reaction of Ph2GeMn(C0)4COMe with sodium methoxide is presumed to involve nucleophilic attack at germanium to give a methoxygermanium species. Subsequent treatment with aqueous tetraethylammonium bromide gave the hydroxygermanium complex, [cis-Ph2(HO)-GeMn(C0)4C (0) 54, 2557 (1976). On a prkpark plusieurs sels acylates et plusieurs complexes de carbene non cyclique du manganbe et du rhknium contenant des ligands organogermanium en faisant intervenir les rB actions de complexes de germoxycarbkne cyclique de structure brute Ph2GeM(CO)4COMe (M = Mn, Re) avec les nuclkophiles methyllithium ou ion methylate. Dans chaque cas, le produit observk peut &tre rationalisk en terme d'une attaque nuclkophile au site du germanium. La rhction du Ph2GeRe(C0)4COMe avec le mCthyllithium suivi par une rhction d'kthylation avec le Et30BF4 aqueux conduit au Ph2MeGeRe(C0)4C(OEt)Me cis. On peut aussi obtenir I'analogue avec du manganbe de ce composk si l'on utilise un excb de mkthyllithium dans la premikre ktape. L'utilisation d'une quantitk dkficiente de mkthyllithium suivie par une kthylation conduit toutefois au Ph2FGeMn(C0)4C(OEt)Me cis. Des spectres infrarouges en solution indiquent que des impuretk de mkthylate de lithium et de bromure de lithium dans le mkthyllithium sont impliquks dans cette rhction. On fait I'hypothbe que la rhction du Ph2GeMn-(C0)4COMe avec le mkthylate de sodium implique une attaque nuclkophile au niveau du germanium pour conduire ? I des espkces mkthoxygermanium. Un traitement ultkrieur avec du bromure de tktrakthylammonium aqueux conduit au complexe hydroxygermanium [Phl(OH)-GeMn(CO)4C (0) IntroductionIn recent papers we have described the synthesis and characterisation of a number of carbene complexes of manganese and rhenium which also contain organogermanium or organotin ligands. A number of compounds with an unusual cyclic structure of the type 1 have been

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Stereoselectivity in the Reactions of Nitrosopiperidine Carbanions. Steric vs. Stereoelectronic Control

Cited by 39 publications

References 17 publications

Conformational analysis of ketoximes by the application of carbon-13 nuclear magnetic resonance spectroscopy

Conformational analysis of ketoximes by the application of carbon-13 nuclear magnetic resonance spectroscopy

Generation, structure and reactivity of tertiary organolithium reagents

The reactivity of cyclic germoxycarbene complexes of manganese and rhenium towards nucleophiles

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