The Mechanism of Hydrolysis of Imidate Salts. The Importance of Stereoelectronic Control and pH of the Reaction Medium on the Cleavage of Tetrahedral Intermediates

Abstract

PIERRE DESLONGCHAMPS and ROLAND J. TAILLEFER. Can. J. Chem. 53,3029 (1975). Hydrolysis of anti imidate salts give the ester amine products exclusively over the entire range of pH. Hydrolysis of syn imidate salts in acidic and neutral conditions give the ester amine products only; in basic conditions, mixtures of ester amine and amide alcohol products are observed. These results are explained by the application of the new theory of stereoelectronic control on the various ionic forms T + , T + , and T -of the tetrahedral intermediate. L'hydrolyse des sels imidates anti conduit toujours aux produits ester amine quelque soit le p H du milieu rkactionnel. En milieu acide ou legerement basique, les sels imidates syn donnent uniquement les produits ester amine. En milieu basique, ils donnent des melanges des produits ester amine et amide alcool. Ces rtsultats sont expliques par la nouvelle theorie de contr6le stertotlectronique au niveau de I'intermediaire tttrahedrique et par les diverses formes ioniques T+, T* et T -que peut prendre cet intermediaire. De plus, dans le cas des imidates syn, il faut aussi postuler des changements conformationnels de l'intermediaire tktrahdrique pour qu'il puisse se briser avec contr6le stertotlectronique.We have described recently a new theory of stereoelectronic control for the cleavage of tetrahedral intermediates which are formed during the hydrolysis of esters (I), and amides (2-4). In this new theory, the precise conformation of the tetrahedral intermediate (hemiorthoester or hemiorthoamide) plays a major role in determining the products formed. It is postulated that the precise conformation of the tetrahedral intermediate is transmitted into the products of the reaction and that the specific decomposition of such an intermediate is controlled by the orientation of the lone pair orbitals of the heteroatoms. Stereoelectronic cleavage of a tetrahedral intermediate is defined in the following way: specific cleavage of a carbon-oxygen or a carbon-nitrogen bond which occurs when two heteroatoms (oxygen or nitrogen) of the tetrahedral intermediate each have an orbital oriented antiperiplanar to the departing 0-alkyl or Nalkyl leaving group. ' We have reported a study of the basic hydrolysis of several imidate salts having either a syn or an anti conformation (2, 3). The stereoelectronic 'Theoretical calculations have been carried out and support this theory (5).theory predicts that an imidate salt having an anti conformation such as 1A (Scheme 1) will react with hydroxide ion to give the tetrahedral conformer 2A. Conformer 2A has a lone pair orbital on each oxygen properly oriented so that it can be cleaved with stereoelectronic control to yield the ester amine products. The theory also implies that when a tetrahedral intermediate can break down in a stereoelectronically controlled fashion, the energy barrier for its cleavage is much lower than that for rotation to give other conformers. So, there is no need to consider conformers other than 2A with an anti imidate salt. Such salts sh...

Synthesis of cis-/All-cis-Substituted Cyclopropanes through Stereocontrolled Metalation and Pd-Catalyzed Negishi Coupling

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Synthesis of enantiopure 2‐aryl‐2‐methoxypropionic acids and determination of their absolute configurations by X‐ray crystallography

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“…The mechanism of the hydrolysis of imidate salts has been well studied (for the mechanism of the hydrolysis of imidate salts). [16][17][18] For example, the hydrolysis of an imidate salt with a mild base like aqueous NaHCO 3 yielded ester, but not amide, indicating that the CÀ ÀN bond cleaves first (for the mechanism of the hydrolysis of imidate salts). 18 Therefore, as shown in Scheme 4, the reaction proceeds through the intermediate 30b, in which the CÀ ÀN bond cleaves first with the participation of water affording ester intermediate 30c.…”

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