TY - JOUR

T1 - Kinetic studies for amination of ketenimines

T2 - change of rate-determining step by electron-withdrawing N-substituents through electronic effects

AU - Sung, Kuangsen

AU - Huang, Pin Mei

AU - Chiang, Shu Min

N1 - Funding Information:
This work is supported by NSC of Taiwan, ROC (NSC 94-2113-M-006-009).

PY - 2006/5/15

Y1 - 2006/5/15

N2 - 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 ρD=ρ1=7.08 and ρA=ρK+ρ2=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.

AB - 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 ρD=ρ1=7.08 and ρA=ρK+ρ2=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.

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U2 - 10.1016/j.tet.2006.03.022

DO - 10.1016/j.tet.2006.03.022

M3 - Article

AN - SCOPUS:33646028811

VL - 62

SP - 4795

EP - 4799

JO - Tetrahedron

JF - Tetrahedron

SN - 0040-4020

IS - 20

ER -