Reactions of N-(arylsulfonoxy)-N-alkylbenzylamines with MeONa-MeOH. Steric effect on the structure of the imine-forming transition state

Bong-Rae Cho, Sang Yong Pyun

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Abstract

Elimination reactions of N-(arylsulfonoxy)-N-alkylbenzylamines 1-5 with MeONa-MeOH have been studied kinetically. The elimination reactions are regiospecific, producing only corresponding benzylidenalkylamines. The rate equation for the reactions is kobs = k0 + k2[MeONa], indicating that the reactions proceed by competing solvolytic- and base-promoted pathways. The relative rates of elimination for the k2 and k0 pathways are 1, 0.67, 0.53, 0.35, and 0.27 for R = Me, Et, i-Pr, s-Bu, and t-Bu and 1, 4.1, 5.1, and 8.7 for R = Et, i-Pr, s-Bu, and t-Bu, respectively. For MeONa-promoted elimination from 1-5, Hammett ρ and kH/kD decrease but ρ1g and |β1g| increase with a bulkier alkyl substituent. However, the values for the solvolytic eliminations are nearly the same for all substrates and are similar to those for the base-promoted pathway, except for the ρ values, which have opposite signs. From these results, the changes in transition-state structure wrought by variation of N-alkyl substituents are assessed.

Original languageEnglish
Pages (from-to)3920-3924
Number of pages5
JournalJournal of the American Chemical Society
Volume113
Issue number10
Publication statusPublished - 1991 May 8

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title = "Reactions of N-(arylsulfonoxy)-N-alkylbenzylamines with MeONa-MeOH. Steric effect on the structure of the imine-forming transition state",
abstract = "Elimination reactions of N-(arylsulfonoxy)-N-alkylbenzylamines 1-5 with MeONa-MeOH have been studied kinetically. The elimination reactions are regiospecific, producing only corresponding benzylidenalkylamines. The rate equation for the reactions is kobs = k0 + k2[MeONa], indicating that the reactions proceed by competing solvolytic- and base-promoted pathways. The relative rates of elimination for the k2 and k0 pathways are 1, 0.67, 0.53, 0.35, and 0.27 for R = Me, Et, i-Pr, s-Bu, and t-Bu and 1, 4.1, 5.1, and 8.7 for R = Et, i-Pr, s-Bu, and t-Bu, respectively. For MeONa-promoted elimination from 1-5, Hammett ρ and kH/kD decrease but ρ1g and |β1g| increase with a bulkier alkyl substituent. However, the values for the solvolytic eliminations are nearly the same for all substrates and are similar to those for the base-promoted pathway, except for the ρ values, which have opposite signs. From these results, the changes in transition-state structure wrought by variation of N-alkyl substituents are assessed.",
author = "Bong-Rae Cho and Pyun, {Sang Yong}",
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T1 - Reactions of N-(arylsulfonoxy)-N-alkylbenzylamines with MeONa-MeOH. Steric effect on the structure of the imine-forming transition state

AU - Cho, Bong-Rae

AU - Pyun, Sang Yong

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N2 - Elimination reactions of N-(arylsulfonoxy)-N-alkylbenzylamines 1-5 with MeONa-MeOH have been studied kinetically. The elimination reactions are regiospecific, producing only corresponding benzylidenalkylamines. The rate equation for the reactions is kobs = k0 + k2[MeONa], indicating that the reactions proceed by competing solvolytic- and base-promoted pathways. The relative rates of elimination for the k2 and k0 pathways are 1, 0.67, 0.53, 0.35, and 0.27 for R = Me, Et, i-Pr, s-Bu, and t-Bu and 1, 4.1, 5.1, and 8.7 for R = Et, i-Pr, s-Bu, and t-Bu, respectively. For MeONa-promoted elimination from 1-5, Hammett ρ and kH/kD decrease but ρ1g and |β1g| increase with a bulkier alkyl substituent. However, the values for the solvolytic eliminations are nearly the same for all substrates and are similar to those for the base-promoted pathway, except for the ρ values, which have opposite signs. From these results, the changes in transition-state structure wrought by variation of N-alkyl substituents are assessed.

AB - Elimination reactions of N-(arylsulfonoxy)-N-alkylbenzylamines 1-5 with MeONa-MeOH have been studied kinetically. The elimination reactions are regiospecific, producing only corresponding benzylidenalkylamines. The rate equation for the reactions is kobs = k0 + k2[MeONa], indicating that the reactions proceed by competing solvolytic- and base-promoted pathways. The relative rates of elimination for the k2 and k0 pathways are 1, 0.67, 0.53, 0.35, and 0.27 for R = Me, Et, i-Pr, s-Bu, and t-Bu and 1, 4.1, 5.1, and 8.7 for R = Et, i-Pr, s-Bu, and t-Bu, respectively. For MeONa-promoted elimination from 1-5, Hammett ρ and kH/kD decrease but ρ1g and |β1g| increase with a bulkier alkyl substituent. However, the values for the solvolytic eliminations are nearly the same for all substrates and are similar to those for the base-promoted pathway, except for the ρ values, which have opposite signs. From these results, the changes in transition-state structure wrought by variation of N-alkyl substituents are assessed.

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