Ketene-Forming Elimination Reactions from Aryl Thienylacetates Promoted by R<sub>2</sub>NH/R<sub>2</sub>NH<sub>2</sub><sup>+</sup> in 70 mol % MeCN(aq). Effect of the β-Aryl Group
作者:Bong Rae Cho、Sang Yong Pyun
DOI:10.1021/jo0612978
日期:2007.2.1
Ketene-forming eliminations from ArCH2CO2C6H3-2-X-4-NO2 (Ar = thienyl, 1) promoted by R2NH/R2NH2+ in 70 mol % MeCN(aq) have been studied kinetically. When X = CF3 and NO2, the reactions exhibit second-order kinetics as well as β = 0.30−0.64 and |βlg| = 0.31−0.52 that decrease with a better leaving group. Hence, an E2 mechanism is evident. As the leaving group is made poorer (X = H, OCH3, and Cl), E2
在70摩尔%MeCN(aq)中,由R 2 NH / R 2 NH 2 +促进的ArCH 2 CO 2 C 6 H 3 -2-X-4-NO 2(Ar =噻吩基,1)促进了形成烯酮的消除。进行动力学研究。当X = CF 3和NO 2时,反应表现出二级动力学,以及β= 0.30-0.64和| βlg |。= 0.31-0.52,随着离开组的改善而降低。因此,E2机制是显而易见的。由于离去基团变得更贫穷(X = H,OCH 3,以及Cl),E2跃迁状态更趋向于质子转移,正如Brönstedβ增加到0.5-0.64所揭示的那样,并且E1cb机理相互竞争。随着反应物结构的变化,k 1和k -1 / k 2值的变化为竞争的E1cb机制提供了额外的支持。通过与4-YC 6 H 4 CH 2 CO 2 C 6 H 3 -2-X-4-NO 2的现有数据进行比较,评估了β-芳基对乙烯酮形成消除的影响。