Tethered 1,2-Si-Group Migrations in Radical-Mediated Ring Enlargements of Cyclic Alkoxysilanes: An EPR Spectroscopic and Computational Investigation.
J Org Chem
; 82(13): 6886-6894, 2017 07 07.
Article
em En
| MEDLINE
| ID: mdl-28581743
ABSTRACT
5- to 6-member ring enlargements of 3-oxa-2-silacyclopentylmethyl to 4-oxa-3-silacyclohexyl radicals were investigated by EPR spectroscopy and QM computations of model indano-oxasilacyclopentane and oxasilinanyl compounds. Both experimental and computational evidence favored a mechanism via a concerted 1,2-migration of the "tethered" Si-group. Thus, the "forbidden" 1,2-Si-group migration from carbon to carbon becomes allowed when the Si-group is "tethered". The EPR data from 3-oxa-2-silacyclopentylmethyl radicals disclosed ground state conformations having semioccupied p-orbitals close to antiperiplanar with respect to their ß-Si-C bonds, but indicated Si-hyperconjugation (ß-silicon effect) was insignificant in radicals. Kinetic data was obtained by the steady state EPR method for ring enlargement of indano-3-oxa-2-silacyclopentylmethyl radicals. The scope of the novel rearrangement in terms of other ring types and sizes, as well as the analogous 1,2-migration of "tethered" C-centered groups, was explored computationally.
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MEDLINE
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En
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2017
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Article