3-Amino- and 3-acylamido-2-phosphonopyridines: synthesis by Pd-catalyzed P-C coupling, structure and conversion to pyrido[b]-anellated PC-N heterocycles |
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Authors: | Mohamed Shaker S Adam Markus K Kindermann Peter G Jones |
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Institution: | a Institut für Biochemie, Ernst-Moritz-Arndt-Universität Greifswald, Felix-Hausdorff-Strasse 4, 17489 Greifswald, Germany b Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany |
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Abstract: | Palladium catalyzed cross-coupling of 3-amino- and 3-acylamido-2-bromopyridines 1a-f with triethyl phosphite allowed the synthesis of 3-amino- and 3-acylamido pyridine-2-phosphonic acid diethyl esters 2a-f, whereas nickel catalysts, although providing access to related anilido-2-phosphonates, proved inactive. Reduction of the aminophosphonate 2a with LiAlH4 afforded 3-amino-2-phosphinopyridine (3a), which was cyclocondensed with dimethylformamide dimethyl acetal (DMFA) via phosphaalkene intermediates 4a to the novel pyridob]-anellated 1,3-azaphosphole 5a. Reaction of amidophosphonates 2b-f with LiAlH4 did not result in the expected reductive cyclization, as shown by closely related anilido-2-phosphonates, but led to product mixtures containing N-secondary 3-amino-2-phosphinopyridines 3b-f as the main or major component. The conversion of 3b,d,e with DMFA to 5b,d,e provides first examples of N-substituted pyridob]-anellated azaphospholes. Structures were confirmed by multinuclear NMR and X-ray crystallography (for 2c, 3b). |
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Keywords: | Pyridine phosphonates Phosphines Heterophospholes Palladium catalysis Hydrogen bonds |
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