Cyclotriphosphazene derivatives with three different chiral centres: Synthesis, characterization and investigation of their stereogenic properties

Abstract

The mono-spiro cyclophosphazene derivative N3P3Cl4[O(CH2)3NH] (1) was reacted with the unsymmetrical reagent 2-methylaminoethanol to give diastereoisomers containing two different chiral centres, N3P3Cl2[O(CH2)3NH][O(CH2)2NMe] (2–3), which are also trans (2) and cis (3) geometric isomers. Compounds 2 and 3 were reacted separately with another unsymmetrical reagent, N-methyl-1,3-propanediamine, to describe the stereogenic properties of cyclotriphosphazenes combined with three different centres of chirality. The compounds N3P3[O(CH2)3NH][O(CH2)2NMe][HN(CH2)3NMe] (4–7), which are named as trans–trans, trans–cis, cis–cis, cis–trans isomers, respectively, were obtained from these reactions. All the compounds were isolated, column chromatography on silica gel was used to separate the diastereoisomers, and these novel compounds were analyzed by elemental analysis, mass spectrometry and 31P and 1H NMR spectroscopies. Additionally, the structures of compounds 2, 3, 4 and 6 were determined by X-ray crystallography. The enantiomers of all the racemic compounds (2–7) were analyzed by the changes in the 31P NMR spectra on addition of a Chiral Solvating Agent (CSA), (R)-(+)-2,2,2-trifluoro-1-(9′-anthryl)ethanol, to investigate their stereogenic properties. The four diastereoisomeric products 4–7 represent all the possible stereochemical isomers of a cyclotriphosphazene with three different chiral centres.