Inverse electron-demand Diels-Alder reactions of N-sulfonyl .alpha.,.beta.-unsaturated imines: a general approach to implementation of the 4.pi. participation of 1-aza-1,3-butadienes in Diels-Alder reactions

Boger, Dale L.; Corbett, Wayne T.; Curran, Timothy T.; Kasper, Annette M.

doi:10.1021/ja00005a040

Cited by 199 publications

(51 citation statements)

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“…Although the most stable cycloadduct (18) has the same configuration as the diastereomer observed experimentally, the energy differences are small and would be consistent with a poor stereoselectivity.…”

supporting

confidence: 62%

“…Boger has also explained the endo orientation on the basis of a similar hyperconjugative anomeric-type interaction in which the lone pair of electrons on the diene or a dipole oxygen (n O ) interact with the s* CO orbital of the ether, therefore stabilizing the endo TS when arranged in an antiperiplanar arrangement. [18] The TS 9 is less stable (DE 0.52 kcal mol À1 ) because the stabilizing Coulombic interaction does not compensate the steric hindrance of such substituents that become closer.…”

Section: The [42] Cycloadditionðstereochemistrymentioning

confidence: 99%

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Understanding Diastereofacial Selection in Carbohydrate-Based Domino Cycloadditions: Semiempirical and DFT Calculations

et al. 2000

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The sequential cycloaddition of nitroalkenes with methyl vinyl ether was investigated by semiempirical (PM3) and density functional methods (B3LYP/6-31G*). The asymmetric version was also examined with a threoconfigured carbohydrate auxiliary. This produces a larger, more flexible system that complicates the calculation. Most transition structures were then fully optimized at the PM3 level and further refinement was done at ab initio levels. This study represents a model case that enables the rationalization of the high facial selectivity observed in carbohydrate-based nitrone- and nitronate-alkene cycloadditions. The selective endo orientation of the [4+2] pathway results from Coulombic attraction and secondary orbital interactions in the transition state. The stereochemical outcome is largely influenced by a combination of steric shielding from the bulky chiral substituent at C4 and the anomeric effect that places the nitronate C6-alkoxy group in a pseudoaxial arrangement. The resulting conformation favors the subsequent exo approach of methyl vinyl ether to the less hindered re face of the nitronate. It is also remarkable to note that solvation energies stabilize significantly a particular transition structure, thereby explaining the marked stereoselection observed in a polar medium.

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supporting

confidence: 62%

Section: The [42] Cycloadditionðstereochemistrymentioning

confidence: 99%

Understanding Diastereofacial Selection in Carbohydrate-Based Domino Cycloadditions: Semiempirical and DFT Calculations

et al. 2000

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“…2,[7][8][9] However, only few methods are reported for the preparation of N-Sulfonylimines of enolizable and sterically hindered ketones. Such reactions involve the in situ generation of oxime Osulfinyl derivatives 10 and their subsequent homolytic rearrangement to sulfonylimines.…”

Section: Preparationmentioning

confidence: 99%

Synthetic Utility of N-Sulfonylimines

Shukla¹

2009

Synlett

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“…Regarding the ketone partner, its transformation into oximes has allowed successful reactions with both sulfinyl chlorides [17,18] and sulfonyl cyanides [19] to yield N-sulfonyl ketimines. Examples of the opposite approach, involving the modification of the nucleophile, have also been reported: sulfinamides, which are more nucleophilic than sulfonamides, have been condensed with the carbonyl group, followed by oxidation to the desired N-sulfonyl ketimine.…”

Section: Introductionmentioning

confidence: 99%