Zur Synthese von Siloxanen XVI . Die Stereochemie nucleophiler Substitutionen an Si-Atomen substituierter Cyclotrisiloxane

Abstract

1-Substituted 1,3,5-trimethyl-3,5-bis(trimethylsiloxy)cyclotrisiloxanes ([(MT) 2D X]; X = Cl, Br, OAc, OMe, H, OH) were prepared to investigate the stereochemistry of nucleophilic substitution reactions at silicon atoms of cyclosiloxanes. The signals of the 1H and 29Si NMR spectra of these compounds were assigned to the three possible configurational isomers and the proportions of the isomers in the synthesized mixtures were established. The reactions of [(MT) 2D Cl] with alcohols and acetic acid, the bromination of [(MT) 2D H] and the hydrolysis of [(MT) 2D OAc] were studied by 1H and 29Si NMR spectroscopy without separating the isomer mixtures. Taking into account the intensity and the shift of the signals of the structural isomers of educts and products it was possible to determine the relative rate constants of the isomers and the stereochemistry of the reaction. It was found that all investigated reactions proceed with retention of configuration.