Kinetic studies for amination of ketenimines: change of rate-determining step by electron-withdrawing N-substituents through electronic effects

Kuangsen Sung, Pin Mei Huang, Shu Min Chiang

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5 Citations (Scopus)

Abstract

Kinetic studies for the amination of ketenimines 1a-d and 2a-e with n-BuNH2 were carried out by means of UV spectrometry. Hammett equation was applied to the second-order rate constant (k1) for the amination of 2a-e and the Hammett plot demonstrated a linear free-energy relationship with a reaction constant (ρ1) of 2.87, indicating that the second-order rate constant (k1) corresponds to the first step of rate-determining C{double bond, long}N addition. In contrast, Hammett equation was applied to Kk2 for the amination of 1a-d and the Hammett plot was a convex curve with ρD1=7.08 and ρAK2=0.98, indicating change of the rate-determining step. The electron-withdrawing para-substituents on the N-phenyl group of ketenimines significantly stabilize the first transition state of C{double bond, long}N addition, resulting in change of the rate-determining step to the second step of tautomerization. The N-substituent electronic effect has much more significant influence on the amination of ketenimines than the substituent electronic effect at Cβ.

Original languageEnglish
Pages (from-to)4795-4799
Number of pages5
JournalTetrahedron
Volume62
Issue number20
DOIs
Publication statusPublished - 2006 May 15

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Drug Discovery
  • Organic Chemistry

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