Date of Award
Doctor of Philosophy
The regiochemistry of intramolecular cyclization of some alkenylsilyl and alkenyldisilanyl radicals has been examined. It has been demonstrated that the silyl radicals produced by hydrogen abstraction from a pentenylsilane, a butenylsilane, a butenyldisilane, an allyldisilane, and a butenyloxysilane all cyclize in an endo-fashion. This is in complete contrast to what is known for the analogous carbon-centered radicals. No cyclic products are observed for chain lengths shorter than five atoms. Also, when alkenyldisiloxanyl and butadienyl-type silyl radicals are generated by pyrolytic cleavage of silicon-allyl bonds, endo-closure is found to be the exclusive mode of cyclization. However, alkenyldisilanyl radicals undergo disproportionation to silenes when generated by pyrolysis of allyldisilanes. The silenes, formed by what is formally a retroene elimination of propene, afford 1,3-disilacyclics via silene to silylene rearrangement;The pyrolysis of 3-butenylsilanes was found to give (alpha)-silyl radicals via carbon-allyl homolysis of the butenyl groups. A 1,2-hydrogen migration from silicon to a carbon-centered radical has been observed for dimethylsilylcarbinyl radical. The radical was produced from 3-butenyldimethylsilane and afforded the first example of this type 1,2-hydrogen shift. Intramolecular endo-cyclization has also been observed to occur for (alpha)-silyl radicals possessing an alkenyl substituent;The pyrolysis of allyloxysilanes was also examined in a search for precursors to alkenylsilyloxy radicals. From this study, allyloxy-allyldimethylsilane was found to be an excellent dimethylsilanone precursor; the initial step being oxygen-allyl cleavage to the corresponding silyloxy radical.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Revis, Anthony, "The regiochemistry of alkenylsilyl, alkenyldisilanyl and alkenylsilyloxy radical cyclizations " (1984). Retrospective Theses and Dissertations. 9023.