Kinetics and Mechanism of Michael-type Reactions of Ethyl Propiolate with Alicyclic Secondary Amines in H2O and MeCN: Solvent Effect on Reactivity and Transition-State Structure

Bulletin of the Korean chemical society

Ik Hwan Um¹  Song I Kim¹  Hye Won Baek¹ 

关键词: Ethyl propiolate;    Michael-type reaction;    Kinetic isotope effect;    Rate-determining step;    Br©ªnsted-type plot;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

The amines studied in this study are less reactive toward ethyl propiolate (3) in MeCN than in H₂O although they are 7 to 9 pK_a units more basic in the aprotic solvent. The reactivity of morpholine and deuterated morpholine toward 3 is found to be identical, indicating that proton transfer occurs after rate-determining step (RDS). The fact that kinetic isotope effect is absent excludes a stepwise mechanism in which proton transfer occurs in RDS as well as a concerted mechanism in which nucleophilic attack and proton transfer occur concertedly through a 4-membered cyclic transition state (TS). Thus, the reactions have been concluded to proceed through a stepwise mechanism in which proton transfer occurs after RDS. Br┆nsted-type plots are linear with small �?_nuc values, i.e., �?_nuc = 0.29 in H₂O and モnuc = 0.51 in MeCN, indicating that bond formation is not advanced significantly in RDS. The small �?_nuc value also supports the conclusion drawn from the study of kinetic isotope effect.

【 授权许可】

Unknown