Page, Michael I., Webster, Philip S. and Ghosez, Leon (1990) The hydrolysis of azetidinyl amidinium salts. Part 2. Substituent effects, buffer catalysis, and the reaction mechanism. Journal of the Chemical Society, Perkin Transactions 2 (5). pp. 813-823. ISSN 1472-779X

The hydrolysis of azetidin-2-ylideneammonium salts gives a mixture of -lactams, by exocyclic C–N bond fission, and -amino amides, by endocyclic C–N bond breakage and opening of the four-membered ring. The reaction is general-base catalysed and more -lactam is formed using a less basic buffer. The mechanism of the buffer-catalysed reaction is the general-acid-catalysed breakdown of a reversibly formed neutral tetrahedral intermediate. The Brønsted -values vary with substituents in the amidinium salt so that they decrease with increasing electron withdrawal in the nitrogen amine which is expelled. Electron-withdrawing substituents attached to either nitrogen of the amidinium salt favour expulsion of that leaving-group amine. The Brønsted 1g for endocyclic C–N bond fission and -amino amide formation is –0.52 whereas that for exocyclic C–N bond fission and -lactam formation is –0.83. Substituent effects on the nitrogen amine which is not expelled but forms the product amide or -lactam generate p values of –0.71 and –0.07, respectively. Changes in structure–reactivity relationships with substituents are examined by an analysis of the reaction mechanism

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