Ketene-Forming Elimination Reactions from Aryl Thienylacetates Promoted by R2NH in MeCN. Effects of Base-Solvent and ¥â-Aryl Group

Bulletin of the Korean chemical society

Bong Rae Cho¹  Sang Yong Pyun¹  Ju Chang Kim¹  Eun Ju Cho¹  Seok Hee Lee¹  Hyoun Jung Seok¹ 

关键词: Elimination;    E2;    ¥â-Aryl group effect;    Mechanism;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

Ketene-forming eliminations from C₄H₃(S)CH₂C(O)O-C₆H₃-2-X-4-NO₂ (1) promoted by R₂NH in MeCN have been studied kinetically. The reactions are second-order and exhibit Bronsted �? =0.51-0.62 and |�?_lg|= 0.47-0.53. Hence, an E2 mechanism is evident. The Bronsted �? increased from 0.33 to 0.53 and |�?_lg| remained nearly the same by the change of the base-solvent from Bz(i-Pr)NH/Bz(i-Pr)NH₂⁺ in 70 mol% MeCN(aq) to Bz(i-Pr)NH-MeCN, indicating a change to a more symmetrical transition state with similar extents of C_�? -H and C_�? -OAr bond cleavage. When the �?-aryl group was changed from thienyl to phenyl in MeCN, the �? value increased from 0.53 to 0.73 and |�?_lg| decreased from 0.53 to 0.43. This indicates that the transition state became skewed toward more C_�? -H bond breaking with less C_�?-OAr bond cleavage. Noteworthy is the greater double bond stabilizing ability of the thienyl group in the ketene-forming transition state.

【 授权许可】

Unknown