Reactivity and Mechanism in the Hydrolysis of -Sultams

详细信息    查看全文

• 作者：Nicholas J. Baxter ; Laurent J. M. Rigoreau ; Andrew P. Laws ; and Michael I. Page
• 刊名：Journal of the American Chemical Society
• 出版年：2000
• 出版时间：April 12, 2000
• 年：2000
• 卷：122
• 期：14
• 页码：3375 - 3385
• 全文大小：339K
• 年卷期：v.122,no.14(April 12, 2000)
• ISSN：1520-5126

文摘

-Sultams show extraordinary rate enhancements of 10⁹- and 10⁷-fold, respectively, compared withthe acid- and base-catalyzed hydrolysis of corresponding acyclic sulfonamides. They are about 10³-fold morereactive than analogous -lactams. The alkaline hydrolysis of some -sultams shows a rate term that is second-order in hydroxide ion concentration, which is indicative of a stepwise mechanism involving a trigonalbipyramidal intermediate (TBPI). The Brnsted _lg value for the alkaline hydrolysis of N-aryl--sultams is-0.58 and the kinetic solvent isotope effect / is 0.60, compatible with rate-limiting formation of theTBPI. Conversely, / for N-alkyl--sultams is 1.55, indicative of rate-limiting breakdown of the TBPI.The acid-catalyzed hydrolysis of -sultams is strongly retarded by electron-withdrawing groups to the sulfonylgroup, and it is suggested that the mechanism may involve unimolecular ring opening to generate a sulfonyliumion. The Brnsted _lg value for the acid-catalyzed hydrolysis of N-benzyl--sultams is 0.32. The general-acid-catalyzed hydrolysis of N-benzyl--sultam by carboxylic acids shows a Brnsted value of 0.67 and isattributed to a specific acid-nucleophilic mechanism with the formation of a mixed-anhydride intermediate.