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Isoxazole Strategy for the Synthesis of 2,2′-Bipyridine Ligands: Symmetrical and Unsymmetrical 6,6′-Binicotinates, 2,2′-Bipyridine-5-carboxylates, and Their Metal Complexes
An effective strategy was developed for the synthesis of new 2,2′-bipyridine ligands, symmetrical and unsymmetrical 6,6′-binicotinates, and 2,2′-bipyridine-5-carboxylates, from 4-propargylisoxazoles. The synthesis of symmetrical 2,2′-disubstituted 6,6′-binicotinates was achieved using the Eglinton r...
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Published in: | Journal of organic chemistry 2019-03, Vol.84 (6), p.3524-3536 |
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Main Authors: | , , , , , , |
Format: | Article |
Language: | English |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | An effective strategy was developed for the synthesis of new 2,2′-bipyridine ligands, symmetrical and unsymmetrical 6,6′-binicotinates, and 2,2′-bipyridine-5-carboxylates, from 4-propargylisoxazoles. The synthesis of symmetrical 2,2′-disubstituted 6,6′-binicotinates was achieved using the Eglinton reaction of 5-methoxy-4-(prop-2-yn-1-yl)isoxazoles with Cu(OAc)2, followed by Fe(NTf2)2/Au(NTf2)tBuXPhos-catalyzed isomerization of the so-formed mixture of isoxazole/azirine-substituted biacetylenic intermediates. Unsymmetrical 2,2′-disubstituted 6,6′-binicotinates were prepared via a copper-free Sonogashira coupling of 5-methoxy-4-(prop-2-yn-1-yl)isoxazoles with 6-bromonicotinates to give methyl 6-(3-(5-methoxyisoxazol-4-yl)prop-1-ynyl)pyridine-3-carboxylates, followed by a transformation of the propargylisoxazole moiety of the adduct into the pyridine fragment under Fe(II)/Au(I) relay catalysis conditions. 6-(Pyrid-2-yl)nicotinates were synthesized by a Stille-type coupling of 2-(tributylstannyl)pyridine with 6-bromonicotinates. Several cyclopalladated complexes of a new series of 6,6′-binicotinates and 2,2′-bipyridine-5-carboxylates and the homoleptic Cu(I) complex were synthesized in high yields. |
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ISSN: | 0022-3263 1520-6904 |
DOI: | 10.1021/acs.joc.9b00115 |