The Importance of Conformation of the Tetrahedral Intermediate in the Hydrolysis of Amides. Selective Cleavage of the Tetrahedral Intermediate Controlled by Orbital Orientation

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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...

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confidence: 94%

“…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)(3)(4). In this new theory, the precise conformation of the tetrahedral intermediate (hemiorthoester or hemiorthoamide) plays a major role in determining the products formed.…”

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confidence: 99%

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

Deslongchamps¹,

Taillefer²

1975

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“…It was also observed that the fragmentation of the resulting tetrahedral hydrotrioxide intermediates is also conformation dependent and the results could also be rationalized on the basis of stereoelectronic effects. Further studies (9,10) on the stereocontrolled fragmentation of various tetrahedral intermediates were carried out in our laboratory and this work led us to propose a new general theory for the understanding of hydrolytic processes, which is primarily based on stereoelectronic principles (1 1-13). Consequently, this completely unexpected annoying result led to the discovery of a rather fruitful event!…”

Section: Introductionmentioning

confidence: 99%

The total synthesis of (+)-ryanodol. Part III. Preparation of (+)-anhydroryanodol from a key pentacyclic intermediate

Deslongchamps¹,

Bélanger²,

Berney³

et al. 1990

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. Can. J. Chem. 68, 153 (1990 On rapporte plusieurs etudes qui ont conduit a la transformation de l'intemediaire-clC pentacyclique optiquement actif 5 en (+)-anhydroryanodol(6). Cette transformation de 24 Ctapes fait intervenir les intermediaires suivants : 5 + 11 + 19-34+ 36 + 39+ 144+ 150 + 6. La preparation de l'intermediaire-clt pentacyclique 5 est rapportee dans les Parties I et I1 de la prtsente serie.

“…'Undergraduate summer student, 1977. 3Revision received June 6, 1979. control of reactivity was later extended to the breakdown of tetrahedral intermediates formed during the hydrolysis of orthoesters (3,4), imidate salts (3,5), esters, and amides (3,6). In view of the fact that stereoelectronic control of reactivity may be important in many other reactions (3), including reaction of phosphate diesters (7), and reactions of biological interest (S), it seemed important to investigate further the mechanism of oxidation of acetals by ozone.…”

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confidence: 99%

An isokinetic relationship in the oxidation of acetals by ozone. Evidence for rotation before the oxidation of acyclic acetals

Taillefer¹,

Thomas²,

Nadeau³

et al. 1979

Chem. 57,3041 (1979).Second order rate constants for thc oxidation by ozone of several acyclic acetals of heptaldehyde were determined at several temperatures. An isokinetic relationship is shown to exist for this series of reactions and the isokinetic temperature was found to be below the experimental temperature range, a domain of temperatures where reactivity is dominated by entropy factors. These results are contrasted with those obtained for cyclic acetals of heptaldehyde, where the isokinetic temperature falls above the working temperatures, a domain of temperatures where reactivity depends mainly on enthalpy factors. These results are interpreted in terms of a conformational change before oxidation in the acyclic acetals.ROLAND J. TAILLEFER, SHIRLEY E. THOMAS, YVES NADEAU et HELMUT BEIERBECK. Can. J. Chem. 57,3041 (1979).Les constantes de vitesse de deuxieme ordre pour l'oxydation par l'ozone de plusieurs acetales acycliques du heptaldehyde ont t t t dtterminees a plusieurs tempkratures. Ceci a permis de mettre en evidence I'existence d'une relation isocinetique pour cette serie de rtactions. La temperature isocinttique trouvCe est infirieure au domaine de temptratures expirimentales. Ceci correspond a un domaine de temperatures ou la rkactivite depend essentiellement de A S * . Ces resultats sont en opposition avec ceux de l'oxydation d'acttales cycliques du heptaldehyde ou la temperature isocinetique est superieure aux tempkratures expkrimentales, donc dans un domaine de temperatures oh la rtactivite depend essentiellement de AH*. Ces resultats sont interprttts en invoquant un changement conformationnel dans les acetales acycliques avant l'etape d'oxydation.