Synthesis 2016; 48(21): 3773-3784
DOI: 10.1055/s-0035-1561660
paper
© Georg Thieme Verlag Stuttgart · New York

Synthesis and Hydrolysis of 4-Chloro-PyMTA and 4-Iodo-PyMTA Esters and Their Oxidative Degradation with Cu(I/II) and Oxygen

Mian Qi
Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany   Email: godt@uni-bielefeld.de
,
Miriam Hülsmann
Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany   Email: godt@uni-bielefeld.de
,
Adelheid Godt*
Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany   Email: godt@uni-bielefeld.de
› Author Affiliations
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Publication History

Received: 03 March 2016

Accepted after revision: 02 May 2016

Publication Date:
29 June 2016 (online)


Abstract

We disclose the syntheses of ethyl and tert-butyl esters of 4-chloro-PyMTA and 4-iodo-PyMTA from the commercially available chelidamic acid monohydrate in 39–67% overall yield. Additionally, ester hydrolyses with aqueous NaOH (ethyl esters) or trifluoroacetic acid (tert-butyl esters) are reported. The resulting materials contain 4-halo-PyMTA in mixture with partially deprotonated or partially protonated 4-halo-PyMTA. The ligand content expressed as the content of the common structural motifs of the present species, namely [PyMTA – 4 H+]4– (basic hydrolysis) and PyMTA (acidic hydrolysis), was determined to be 90–94 wt % by 1H NMR spectroscopy using maleic acid as an internal standard. The tert-butyl esters were easily hydrolyzed with aqueous alkali hydroxide, with a decreasing rate in the series NaOH, KOH, LiOH. This finding indicates a Lewis acid assisted ester cleavage with the Na+ ion fitting best to the multidentate ligand. Unexpectedly, PyMTA esters are incompatible with Cu(I/II) salts in the presence of oxygen. Under these conditions, one of the two aminomethyl groups is converted into a formyl group. This reaction not only limits the application of Cu(I/II)-catalyzed reactions but also necessitates trapping of any copper ions (e.g., with a metal ion scavenger) before the material is exposed to oxygen.

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