Stereochemical aspects of cyclotriphosphazenes: Prochiral and pseudo-asymmetric phosphorus atoms

Abstract

Mono-, di- and trispiro derivatives (2-6) from the reaction of hexachlorocyclotriphosphazene, (1) with 3-aminobenzyl alcohol were reported in order to illustrate stereochemical terms such as prochiral, pseudo asymmetry, homo-, enantio- and diastereotopic atoms or groups. The dispiro derivatives (3 and 4) were shown to exist as trans and cis geometric isomers and be racemic (RR/SS) and meso (RS), respectively, whereas the trispiro derivatives (5 and 6) exist as cis and trans geometric isomers and are achiral. Pseudo-asymmetry was introduced into the meso form (4) containing two constitutionally equivalent chiral units by the reactions with either 3-amino-1-propanol or phenol. The two meso diastereoisomeric forms, which can be assigned as R,s,S (7a) and R,r,S (7b) or S,s,R (8a) and S,r,R (8b), were identified as the systematic examples of cyclophosphazene derivatives including pseudo-asymmetric phosphorus centers. The corresponding racemic form (3) produced only one diastereoisomer (9 and 10) for each reaction. All the compounds were analysed by standard spectroscopic techniques, such as elemental analysis, MALDI-TOF mass spectrometry, NMR spectroscopy and X-ray crystallography (for 2, 4 and 6). The stereogenic properties of the compounds were confirmed by P-31 NMR spectroscopy on addition of the chiral solvating agent (CSA) (R)-(+)-2,2,2-trifluoro-1-(90-anthryl)ethanol. (C) 2017 Elsevier Ltd. All rights reserved.