Abstract
All- cis-2,4,6,8-tetramethyl-2,4,6,8-tetrakis(triphenylsiloxy)cyclotetrasiloxane ( 4) and syn-1,3,9,11-tetramethyl-5,5,7,7,13,13,15,15-octaphenyltricyclo[9.5.1.1 3,9]octasiloxane ( 5) were synthesized by the reaction of cis,trans,cis-[MeSi(NCO)O] 4 ( 1) with Ph 3SiOH ( 2) and [Ph 2Si(OH)] 2O ( 3), respectively, in the presence of pyridine for the sake of investigating the synthesis of ladder polysilsesquioxanes with perfect siloxane frameworks. Their stereostructures were confirmed by nuclear magnetic resonance spectra and X-ray crystallography, which revealed that 4 and 5 did not retain the stereostructure of the precursor 1. This result was caused by the racemization of 1 with pyridine, and a subsequent nucleophilic substitution reaction of 1 with 2 or 3, including inversion and retention of the configuration at the silicon atoms.
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