Chemistry of carbanions. XXVI. Synthesis of certain .gamma.-alkenyl, .alpha.,.beta.-unsaturated ketones

ROBERT R. FRASER and NOEMI CHUAQUI-OFFERMANNS. Can. J. Chem. 59,3007 (1981). The "C shieldings for a series of aldimines and ketimines have been measured along with the shifts for their 1-lithio derivatives. For those aldimines with a primary or secondary alkyl group attached to nitrogen, the "lithiation shifts" for the attached carbon (C-4) were all upfield due to the change from anti to syn configuration on lithiation. In the ketimines and in the N-tert-butyl aldimines and ketimines. the lithiation shifts for the C-4 carbon failed to provide stereochemical information. The shifts at C-1 and C-2 proved similar to those previously observed for lithiated alkenes.ROBERT R. FRASER et NOEMI CHUAQUI-OFFERMANNS. Can. . I . Chem. 59, 3007 (1981). On a mesure les blindages du I3C d'une serie d'aldimines et de cetimines ainsi que les deplacements chimiques de leurs derives lithies en position 1. Pour les aldimines ayant un groupe alkyle primaire ou secondaire fixe sur I'azote, les deplacements conduits par la lithiation du carbone (C-4) se font tous vers les champs forts par suite d'un changement de configuration de anti a syn lors de la lithiation. Dans le cas des cetimines, des N-butylaldimines et cetimines, les deplacements provoques par la lithiation sur le carbone en position 4 n'ont pas apporte d'information sur la stereochimie. Les deplacements chimiques des carbones en positions 1 et 2 sont identiques a ceux observes anterieurement pour les derives lithies des aicenes.[Traduit par ie journal]In a series of studies of the stereochemistry of lithiation and alkylation of aldimines and ketimines, we have described evidence for a very marked energetic preference for the formation of a synl lithiated intermediate on the basis of formation of syn alkylation pmducts (1, 21, a b initio calculations (31, and the observation of extraordinarily large barriers to rotation about the N-C-4 single bond of several 1-lithio-3-azapent-2-enides (4). Distinction between configurations at the C=N bond of these imines having the formulae shown below is readily provided by the large syn-anti differential shielding which appears as preferential upfield shifts of 5 to 11 ppm ( 5 ) for either C-1 or C-4 when syn to each other.In this paper we wish to describe the 13C shielding parameters for a variety of lithiated imines. Comparison with the shieldings of their neutral precursors provides a measure of the "lithiation shifts" whose magnitudes appear to be significantly influenced by substituent effects and by the stereochemistry at the C=N bond. A more unique class of sterically congested aldimines and ketimines bearing an N-tert-butyl substituent was also studied. One of these, acetone N-tert-butylimine was observed to undergo lithiation and methylation to give only syn product, indicative of a syrz lithiated intermediate. Unfortunately, similar alkylation experiments on N-tert-butylaldimines were i n c~n c l u s i v e .~ Measurement of the I3C spectra of these aldimines and lithio derivatives gave "lithiation shift" data which failed to p...

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“…The product, bp 64°C (18Torr) exhibited proton and "C nmr properties (5) consistent with structure. Imine 14 has been described previously (7).…”

Section: Methodsmentioning

confidence: 99%

¹³C lithiation shifts in aldimines and ketimines. Evidence on the configuration of lithiated N-tert-butylimines

Fraser¹,

Chuaqui-Offermanns²

1981

Can. J. Chem.

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“…In this context, the catalytic direct a-alkylation of nonstabilized aldehydes and ketones is challenging due to competing side reactions, such as aldol condensations, Cannizzaro and Tishchenko reactions, and N-or O-alkylations. [2,3] Therefore, metal-catalyzed methods that rely on the stoichiometric use of preactivated aldehydes and ketones as their metal enolates, [4] silyl enol ethers, [5] enol carbonates, [6] or enamines [7] have been developed. There are a few methods for the catalytic intermolecular a-alkylation of nonactivated aldehydes and ketones.…”

Section: Ismail Ibrahem and Armando Córdova*mentioning

confidence: 99%

Direct Catalytic Intermolecular α‐Allylic Alkylation of Aldehydes by Combination of Transition‐Metal and Organocatalysis

2006

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“…(6). of 3.67 g (28.93 mmol) of N-( tert-huryl~-Z-methylpropan-l-imine (5) [9] in 15 ml of THF was added dropwise. of 5.7 ml(43.45 mmol) of abs.…”

Section: (-12 (+)-I4mentioning

confidence: 99%

Synthesis and Odor of Chiral Partial Structures of Khusimone. Part 1

Sprdizer

Pichler

Hölzer

et al. 1997

Helvetica Chimica Acta

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Khusimone (1), one of the main odor‐donating compounds of vetiver oil is subject of the following study on structure/odor relationship. The omittance of the ethano bridge of the tricyclic khusimone leads to a bicyclic system. The stereoselective approach to this degraded structure is described, and the olfactory properties are studied. The key step of the synthesis of the hydrindane nucleus is based on a highly diastereoselective conjugate addition to a chiral oxo‐cyclopentene‐2‐carboxylate.

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Chemistry of carbanions. XXVI. Synthesis of certain .gamma.-alkenyl, .alpha.,.beta.-unsaturated ketones

Cited by 64 publications

References 8 publications

¹³C lithiation shifts in aldimines and ketimines. Evidence on the configuration of lithiated N-tert-butylimines

¹³C lithiation shifts in aldimines and ketimines. Evidence on the configuration of lithiated N-tert-butylimines

Direct Catalytic Intermolecular α‐Allylic Alkylation of Aldehydes by Combination of Transition‐Metal and Organocatalysis

Synthesis and Odor of Chiral Partial Structures of Khusimone. Part 1

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Chemistry of carbanions. XXVI. Synthesis of certain .gamma.-alkenyl, .alpha.,.beta.-unsaturated ketones

Cited by 64 publications

References 8 publications

13C lithiation shifts in aldimines and ketimines. Evidence on the configuration of lithiated N-tert-butylimines

13C lithiation shifts in aldimines and ketimines. Evidence on the configuration of lithiated N-tert-butylimines

Direct Catalytic Intermolecular α‐Allylic Alkylation of Aldehydes by Combination of Transition‐Metal and Organocatalysis

Synthesis and Odor of Chiral Partial Structures of Khusimone. Part 1

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¹³C lithiation shifts in aldimines and ketimines. Evidence on the configuration of lithiated N-tert-butylimines

¹³C lithiation shifts in aldimines and ketimines. Evidence on the configuration of lithiated N-tert-butylimines