The structural and stereogenic properties of pentaerythritoxy-bridged cyclotriphosphazene derivatives: spiro–spiro, spiro–ansa and ansa–ansa isomers

Abstract

Reactions of pentaerythritol with hexachlorocyclotriphosphazene, N3P3Cl6, and gem-disubstituted cyclotriphosphazene derivatives, N3P3Cl4R2 [R = Ph, NHBu(t) or (OCH2CF2CF2CH2O)0.5] gave a series of pentaerythritol-bridged derivatives linked spiro-spiro, spiro-ansa and ansa-ansa. The structures and stereogenic properties of the products were characterised by X-ray crystallography and 31P NMR spectroscopy on addition of the chiral solvating agent, (S)-(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol. Molecules with spiro-spiro and spiro-ansa bridged gem-disubstituted cyclophosphazenes [R = Ph, NHBu(t) or (OCH2CF2CF2CH2O)0.5] are found to be chiral and exist as racemates. Molecules with ansa-ansa bridged cyclophosphazenes [R = Cl or (OCH2CF2CF2CH2O)0.5] have been characterised for the first time and are shown to have meso configurations. Analysis of crystal structure data shows that the six-membered chair form of the spiro rings and the eight-membered boat-chair form of the ansa rings in the bridged compounds are similar to analogous spiro and ansa exocyclic ring conformations of 1,3-propanedioxy-derivatives of cyclophosphazenes.

Chiral configurations in cyclophosphazene chemistry

“…1:2:1 for 139a : b : c, respectively [38]. These results are consistent with the assumption that, at each stage of the reaction, 1,3-aminopropanol reacts with a PCl 2 group of a cyclophosphazene ring to form, with equal probability, both the R and S isomers of spiro derivatives and that, as the tri-spirane compound 139 is substituted with two equivalent conventional centers of chirality, compound 139b occurs with twice the probability of its diastereoisomers 139a and c. M a n u s c r i p t 51 …”

“…In the cyclophosphazene literature [21,51] effects with CSR are given at ca. 0.3:1 mole ratio, whereas effects with CSA need at least ca.…”

“…This has been exploited using derivatives of the cyclophosphazene outer rings such as gem-disubstituted [167], cis and trans-1,3-disubstituted [167], spiro and ansa 1,3-propanedioxy disubstituted derivatives [168] and for spiro-spiro, spiro-ansa and ansa-ansa isomers [51]. These observations lead to a more systematic investigation of the stereoegenic properties of trispiranes based on derivatives of compound 137, which resulted in unambiguous quantitative confirmation of the chiral properties of spiranes with two additional centers of chirality and the first characterization of spiranes with four additional centers of chirality.…”

Stereogenic properties of spiranes combined with one or two equivalent conventional centres of chirality

“…31 P NMR spectra were recorded in CDCl 3 solutions on a Bruker DRX 500 MHz spectrometer using 85% H 3 PO 4 as an external reference for 31 P. In order to assign the signals of some compounds both proton-coupled and proton-decoupled 31 P NMR spectra were recorded. Quantitative 31 P NMR spectra were performed with suppression of the NOE and under pulsing conditions (p/3 pulse, overall repetition time of 3.6 s) that allowed for relaxation times of the 31 P nuclei of up to 6 s in spiro-and ansa-substituted cyclophosphazene derivatives [9]. Experiments involving the chiral solvating agent (CSA) were performed by addition of small aliquots of a concentrated solution of CSA in the solvent used for NMR spectroscopy and the proton-decoupled 31 P NMR spectra recorded at each addition.…”

The Reactions of N3P3Cl4[NH(CH2)3NMe] with Difunctional Fluoro Alcohols

“…[1][2][3][4] The four types of products derived from the reactions of cyclotriphosphazenes with diols (spiro, ansa, open chain, and bridged compounds) are well established. 5 Reaction of N 3 P 3 Cl 6 (trimer) with 1,2-ethane-,1,3-propaneand 1,4-butane-diols (in the presence of pyridine to neutralize the HCl formed) predominantly gave spiro derivatives with 5-, 6-, 7-membered phosphate rings, respectively, whereas ansa derivatives were obtained only in small yields.…”