Journal of the Chemical Society. Perkin transactions II p. 813 - 823 (1990)
Update date:2022-07-31
Topics:
Page, Michael I.
Webster, Philip S.
Ghosez, Leon
The hydrolysis of azetidin-2-ylideneammonium salts gives a mixture of β-lactams, by exocyclic C-N bond fission, and β-amino amides, by endocyclic C-N bond breakage and opening of the four-membered ring.The reaction is general-base catalysed and more β-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 Broensted α-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 Broensted β1g for endocyclic C-N-bond fission and β-amino amide formation is -0.52 whereas that for exocyclic C-N bond fission and β-lactam formation is -0.83.Substituent effects on the nitrogen amine which is not expelled but forms the product amide or β-lactam generate βp 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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