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

Abstract

The reactions of hexachlorocyclotriphosphazene, N 3P 3Cl 6, with N/O donor type N-alkyl or (aryl)-o-hydroxybenzylamines HO(C 6H 4)CH 2NHR(Ar), [R(Ar) = C(CH 3) 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.