Stereoselective synthesis of trans N/O dispirocyclic cyclotriphosphazenes based on the steric demands of the constrained 2-pyridyl group |
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| Affiliation: | 1. The School of Chemical Sciences, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia;2. Centre for Nano and Material Sciences, Jain University, Jain Global Campus, Bangalore 562 112, Karnataka, India;1. Gesellschaft für Anlagen- und Reaktorsicherheit GmbH, Theodor-Heuss-Straße 4, 38122 Braunschweig, Germany;2. Institut für Geographie und Geologie, Universität Greifswald, Friedrich-Ludwig-Jahn-Straße 17A, 17487 Greifswald, Germany;3. Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, Schnittspahnstraße 9, 64287 Darmstadt, Germany;4. VNU University of Science, Vietnam National University, Hanoi, 334 Nguyen Trai Road, Thanh Xuan District, Hanoi, Vietnam |
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| Abstract: | Monospiro- and dispirocyclic cyclotriphosphazenes, 2a and 2b, were synthesized by the reaction of hexachlorocyclotriphosphazene, N3P3Cl6 (1), with 2-(2-pyridylamino)phenol in the presence of base. The reactions of phosphazenes 2a and 2b with sodium (4-methyl-2-pyridyl)oxide afforded tetrakis- and bis(4-methyl-2-pyridyloxy)cyclotriphosphazenes, 3a and 3b, respectively. 31P NMR spectroscopy of 2b and 3b using d-camphorsulfonic acid as a chiral solvating agent indicated that they were racemates of the trans isomers. The trans configuration of trans-3b could also be elucidated by X-ray crystal structural analysis, which suggested that the steric demand of the 2-pyridyl group was responsible for the stereoselective formation of trans-2b. The steric demand of the 2-pyridyl group was supported by the reaction of N3P3Cl6 (1) with N,N′-bis(2-pyridyl)benzene-1,2-diamine, which only gave monospirocyclic cyclotriphosphazene 4a. |
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