- Structural effects on reactivity in intramolecular catalysis. The hydrolysis of N-alkylated monoamides derived from norbornene-2,3-dicarboxylic acid
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Monoamides of 2,3-endo-cis-5-norbornene dicarboxylic acid (compounds 1-5) were prepared by addition of primary alkyl amines (n-propyl-, 2-methoxyethyl-, 2-fluoroethyl-, 2,2-difluoroethyl-, 2,2,2-trifluoroethyl-) to 2,3-endo-cis-5-norbornene dicarboxylic anhydride.The rates of hydrolysis of each compound in solutions whose acid concentration ranged from 0.01 M to 9 M were determined.Rates increase with acidity above 0.1 M until a maximum rate is achieved in strong acid.The results are consistent with a mechanism involving intramolecular catalysis of the hydrolysis of the amide by the adjacent carboxylic acid.The dependence of rate on acidity can be interpreted in terms of a multistep mechanism involving formation of an intramolecular tetrahedral adduct, tautomerization of the adduct, and expulsion of the amine to give the anhydride.The identity of the rate-determining step is a function of the basicity of the substrate and the acidity of the medium.Analysis of the data in terms of the proposed mechanism suggests that the effective molarity of the groups involved in tautomerization of the tetrahedral internal addition intermediate is higher than in other rigid systems which lack the norbornene structure.It is proposed that ring strain and rotational entropy control cyclization and elimination steps.Interactions of the solvent with the entire substrate control reorganization of the intermediate.Conjugation of the interacting functional groups does not appear to have a significant effect upon their reactivity.
- Kluger, Ronald,Brandl, Michael
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p. 2515 - 2520
(2007/10/02)
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