Kinetic Study on Michael-type Reactions of 1-Phenyl-2-propyn-1-one with Alicyclic Secondary Amines: Effect of Medium on Reactivity and Mechanism

Bulletin of the Korean chemical society

Ik Hwan Um¹  Youn Min Park¹  So Jeong Hwang¹ 

关键词: Michael-type reaction;    Concerted mechanism;    Stepwise mechanism;    Br©ªnsted-type plot;    Medium effect;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

Second-order rate constants (kN) have been measured for Michael-type addition reactions of a series of alicyclic secondary amines to 1-phenyl-2-propyn-1-one (2) in MeCN at 25.0 �? 0.1 ^oC. All the amines studied are less reactive in MeCN than in H₂O although they are more basic in the aprotic solvent by 7-9 pK_a units. The Br┆nsted-type plot is linear with �?_nuc = 0.40, which is slightly larger than that reported previously for the corresponding reactions in H2O (�?_nuc = 0.27). Product analysis has shown that only E-isomer is produced. Kinetic isotope effect is absent for the reactions of 2 with morpholine and deuterated morpholine (i.e., k^H/k^D = 1.0). Thus, the reaction has been concluded to proceed through a stepwise mechanism, in which proton transfer occurs after the rate-determining step. The reaction has been suggested to proceed through a tighter transition state in MeCN than in H₂O on the basis of the larger �?_nuc in the aprotic solvent. The nature of the transition state has been proposed to be responsible for the decreased reactivity in the aprotic solvent.

【 授权许可】

Unknown