Composes heterocycliques spiranniques—V

Picard, Philippe; Moulines, J.

doi:10.1016/0040-4020(78)88102-2

Cited by 4 publications

(1 citation statement)

References 55 publications

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“…For 16 , the O-axial isomer has been shown to predominate (ca. 68%) in CS 2 solution at 35 °C . This Δ G ° 308 of 0.46 kcal/mol favoring 16a has been attributed to the reduction in syn-axial compression that materializes when the oxygen atom is projected axially.…”

Section: Resultsmentioning

confidence: 98%

π-Facial Diastereoselection in the 1,2-Addition of Allylmetal Reagents to 2-Methoxycyclohexanone and Tetrahydrofuranspiro-(2-cyclohexanone)

Paquette

Lobben

1996

J. Am. Chem. Soc.

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The stereochemical course of the 1,2-addition of several allylmetal reagents and of the Normant Grignard [ClMgO(CH2)3MgCl] to 2-methoxycyclohexanone and tetrahydrofuranspiro-(2-cyclohexanone) has been determined. In four of the six substrates examined, a 4-tert-butyl group is present to serve as a conformational anchor. The neighboring methoxyl substituent is shown to be capable of engaging effectively in chelation, although special circumstances can dictate otherwise. Experiments involving the allylindium reagent as the nucleophile in aqueous solution reveal that the presence of water does not inhibit the operation of chelation control, which often exceeds that attainable with the corresponding magnesium, cerium, and chromium reagents in anhydrous media by significant margins. The extent to which cooperation between the α-oxygen atom and control of π-facial nucleophilic attack reaches a maximum (>97:3) is when the system is conformationally rigid and the 2-methoxy and 4-tert-butyl groups are both oriented equatorially. As the steric bulk about the oxygen is increased, the ability of indium to anchor onto the heteroatom is significantly lessened. The results of competition experiments are detailed. The prospects for useful synthetic applications of indium catalysis in water or water/THF mixtures appear to be very promising.

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Section: Resultsmentioning

confidence: 98%

π-Facial Diastereoselection in the 1,2-Addition of Allylmetal Reagents to 2-Methoxycyclohexanone and Tetrahydrofuranspiro-(2-cyclohexanone)

Paquette

Lobben

1996

J. Am. Chem. Soc.

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Conformer Equilibria in 2,4-Disubstituted Pentane Derivatives

Hoffmann¹,

Stenkamp²,

Trieselmann³

et al. 1999

Eur. J. Org. Chem.

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Flexible molecules with defined shape. Part 3. Conformational analysis of bis(tetrahydropyran-2-yl)methanes

Hoffmann¹,

Kahrs²,

Schiffer³

et al. 1996

J. Chem. Soc., Perkin Trans. 2

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Bis(tetrahydropyran-2-yl)methane 4 along with its racemate have been synthesized. MM3 calculations suggest that the conformer 4a should be populated to cu. 85% in the conformer equilibrium. Analysis of the 'H NMR coupling constants show that one conformer predominates by about 9: 1. That this is the conformer 4a is shown by various NMR techniques, as well as by comparison of calculated with measured CD spectroscopic data. The study is extended to the methyl-substituted bis(tetrahydropyrany1)methanes 2 1 and 23 which show, as predicted from MM3 calculations, essentially monoconformational behaviour.Conformation design aims at the recognition and synthesis of segments of molecular backbones, which are conformationally flexible, but populate predominantly (ie. >90?/~) a single conformation. The starting point for the considerations is a multi-conformational carbon chain. A mono-conformational structure should result if destabilizing interactions could be introduced by structural modification into all but one of the low energy conformations. For instance, pentane has five low energy conformations (Ere, < 3 kcal mol-It) a~ailable.~ Introduction of two methyl groups into the 2 and 4 position reduces the conformational diversity to a bi-conformational situation,' as 2,4-dimethylpentane (1) populates just two enantiomorphic 1 : l c"3*H3

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Composes heterocycliques spiranniques—V

Cited by 4 publications

References 55 publications

π-Facial Diastereoselection in the 1,2-Addition of Allylmetal Reagents to 2-Methoxycyclohexanone and Tetrahydrofuranspiro-(2-cyclohexanone)

π-Facial Diastereoselection in the 1,2-Addition of Allylmetal Reagents to 2-Methoxycyclohexanone and Tetrahydrofuranspiro-(2-cyclohexanone)

Conformer Equilibria in 2,4-Disubstituted Pentane Derivatives

Flexible molecules with defined shape. Part 3. Conformational analysis of bis(tetrahydropyran-2-yl)methanes

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