Microwave-assisted and conventional synthesis and stereogenic properties of monospirocyclotriphosphazene derivatives

The reactions of hexachlorocyclotriphosphazene, N3P3Cl6, with N/O donor type N-alkyl or (aryl)-o-hydroxybenzylamines HO(C6H4)CH2NHR(Ar), [R(Ar) = C(CH3)3 (1), Ph (2)] produce monospirocyclic tetrachlorocyclotriphosphazenes (1a and 2a). The geminal substituted cyclotriphosphazenes (1b, 1d, 2b and 2d) are obtained from the reactions of 1 equiv. of 1a and 2a with 2 equiv. of pyrrolidine or morpholine in THF, while the fully substituted phosphazenes (1c, 1e, 2c and 2e) are formed from the reactions of 1a and 2a with the excess pyrrolidine or morpholine in toluene, between 24 and 48 h. The microwave-assisted reactions of 1a and 2a with excess pyrrolidine or morpholine in toluene afford the fully substituted products with higher yields than those which were obtained by conventional methods. The structural investigations of the compounds have been verified by elemental analyses, ESI-MS, FTIR, 1H, 13C, 31P NMR and HETCOR techniques. The crystal structure of 2a is determined by X-ray crystallography and the phosphazene ring is in the flattened boat form. Compounds 1b, 1d, 2b and 2d in which the spiro aryloxy moiety provides the one centre of chirality exist as racemates and the chirality has been confirmed by 31P NMR spectroscopy on addition of a chiral solvating agent (CSA), (S)-(+)-2,2,2-trifluoro-1-(9′-anthryl)ethanol.

The reactions of N3P3Cl6 with N/O donor type N-alkyl or (aryl)-o-hydroxybenzylamines (1 and 2) afford monospirocyclophosphazenes (1a and 2a). The substituted phosphazenes are obtained from the reactions of 1 and 2 with pyrrolidine (1b, 1c, 2b and 2c) and morpholine (1d, 1e, 2d and 2e). There is one stereogenic P atom in the each of geminal compounds (1b, 1d, 2b and 2d), and the stereogenic properties of these compounds investigated by 31P NMR measurements in the presence of CSA, (S)-(+)-2,2,2-trifluoro-1-(9′-anthryl)ethanol, experiments.Figure optionsDownload as PowerPoint slide