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Issue 5, 2008
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Crossing the threshold from accelerated substitution to elimination with a bifunctional macrocycle

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Abstract

A previously reported macrocyclic amine with anion binding amide residues can be N-alkylated at highly accelerated reaction rates to give quaternary ammonium products. This present study examines the reactivity with 1,2-disubstituted ethanes. Accelerated substitution is observed with 1,2-dichloroethane (5000 times faster than analogous control amines); whereas, accelerated elimination is the outcome with 3-halopropionitriles (10ā€†000 times faster than analogous control amines). The structure of the protonated form of the macrocycle is analyzed by X-ray diffraction. The rates of elimination for 3-chloro, 3-bromo and 3-iodopropionitrile were measured and the relative order of second-order rate constants with triethylamine was 1 : 43 : 182 which reflects the expected order of leaving group abilities. In the case of the macrocycle, the relative order of second-order rate constants was 1 : 29 : 61. The macrocyclic cavity preferentially stabilizes the charge developing on the smaller and more basic Clāˆ’ leaving group. The kinetic data are consistent with a bimolecular syn elimination mechanism.

Graphical abstract: Crossing the threshold from accelerated substitution to elimination with a bifunctional macrocycle

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Publication details

The article was received on 21 Dec 2007, accepted on 07 Feb 2008 and first published on 03 Mar 2008


Article type: Paper
DOI: 10.1039/B719658J
New J. Chem., 2008,32, 843-847

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    Crossing the threshold from accelerated substitution to elimination with a bifunctional macrocycle

    J. J. Gassensmith, J. Lee, B. C. Noll and B. D. Smith, New J. Chem., 2008, 32, 843
    DOI: 10.1039/B719658J

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