CONFORMATION OF EIGHT-MEMBERED DIOXATHIASILOCIN HETEROCYCLES IN SOLUTION
- 1 August 1987
- journal article
- research article
- Published by Taylor & Francis in Phosphorus, Sulfur, and Silicon and the Related Elements
- Vol. 32 (3) , 105-111
- https://doi.org/10.1080/03086648708074268
Abstract
The dibenzo[d,g][1,3,6,2]dioxathiasilocin derivatives 3a-f were prepared by the reaction of the thiobisphenols 1a-b with the corresponding dichlorosilanes 2a-e using triethylamine as an acid acceptor. The free energy of activation for ring inversion of the 2,4,8,10-tetra-tert-butyl-substituted 3a was determined by variable temperature 1H NMR to be 13.9 kcal/mol. The 1H NMR spectral data of 3a requires that the ring conformer possess a σ plane of symmetry passing through the silicon and bridging sulfur atoms. In the variable temperature 1H NMR spectra of the 2,4,8,10-tetramethyl-substituted 3b no evidence was observed for the slowing of ring inversion at-55oC, suggesting that the energy of activation for ring inversion is less than 10.9 kcal/mol. The 1H NMR spectral data of 3e-f indicates the presence of equilibrating conformational isomers. The results of this study supports the suggestion that steric factors are a major contributor to the barrier of ring inversion for the dibenzo-[d, g][1,3,6,2]dioxathiasilocin ring system.Keywords
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