Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5230834 | Tetrahedron | 2006 | 5 Pages |
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 (Ï1) of 2.87, indicating that the second-order rate constant (k1) corresponds to the first step of rate-determining CN addition. In contrast, Hammett equation was applied to Kk2 for the amination of 1a-d and the Hammett plot was a convex curve with ÏD=Ï1=7.08 and ÏA=ÏK+Ï2=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 CN 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.
Graphical abstractDownload full-size image