Stereoisomerism. in pentaerythritol-bridged cyclotriphosphazene tri-spiranes: Spiro and ansa 1,3-propanediyldioxy disubstituted derivatives

Abstract

Four isomeric products were isolated and purified from the reaction of 1,3-propanediol with the tri-spirane cyclophosphazene-organophosphate compound 1: viz. the di-monospiro (2a), di-monoansa (2b) and two monospiro-monoansa derivatives (2c and 2d). It is shown by P-31 NMR spectroscopy on addition of a chiral solvating agent (CSA) that both the di-monospiro 2a and di-monoansa 2b derivatives are racemates, as expected, whereas no splitting of NMR signals occurred on addition of CSA to solutions of 2c and 2d. It is found by X-ray crystallography that the two monospiro-monoansa spirane derivatives, 2c and 2d, are meso diastereoisomers, which represent a new case of the stereochemistry of bis(disubstituted) cyclophosphazene derivatives of 1. It is also observed from the P-31 NMR spectrum of the reaction mixture, supported by the yields of pure compounds, that formation of a spiro group is about 4.5 times more likely than that of an ansa moiety under the conditions of the reaction. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.