Ketene-Forming Elimination Reactions from Aryl Thienylacetates Promoted by R2NH/R2NH2+ in 70 mol % MeCN(aq). Effect of the http://pubs.acs.org/ima

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• 作者：Bong Rae Cho ; Sang Yong Pyun
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：February 16, 2007
• 年：2007
• 卷：72
• 期：4
• 页码：1098 - 1103
• 全文大小：111K
• 年卷期：v.72,no.4(February 16, 2007)
• ISSN：1520-6904

文摘

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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 reactionsexhibit second-order kinetics as well as hars/beta2.gif" BORDER=0 ALIGN="middle"> = 0.30-0.64 and hars/beta2.gif" BORDER=0 ALIGN="middle">_lg = 0.31-0.52 that decrease with a betterleaving group. Hence, an E2 mechanism is evident. As the leaving group is made poorer (X = H, OCH₃,and Cl), E2 transition state becomes more skewed toward the proton transfer, as revealed by the increasein Brönsted hars/beta2.gif" BORDER=0 ALIGN="middle"> to 0.5-0.64, and the E1cb mechanism competes. The changes in the k₁ and k_-1/k₂ valueswith the reactant structure variation provide additional support for the competing E1cb mechanism. Bycomparing with existing data for 4-YC₆H₄CH₂CO₂C₆H₃-2-X-4-NO₂, the effect of hars/beta2.gif" BORDER=0 ALIGN="middle">-aryl group on ketene-forming elimination is assessed.