Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

A number of 1,5-dibromoalkanes have been prepared by using the von Braun degradation method. The ring closure reaction of the diGrignard reagents derived from 1,5-dibromoalkanes and dichlorosilane derivatives were carried out to give C-methylated 1-methyl-1-silasubstituted-1-silacyclohexanes. Since C-methylated 1-chloro-1-substituted-1-silacyclohexanes were available as a mixture in which one isomer predominated greatly, reaction stereochemistry was studied. The stereochemistries of a number of nulceophilic dispalcement reactions of C-methylated 1-methyl-1-silasubstituted-1-silacyclohexane have been investigated. Inversion of configuration was observed upon reduction with LiAlH(,4) in ether, of the chloride, bromide, fluoride and also upon dispalcement of chloride and fluoride with organometallic reagents such as PhLi and PhMgBr. Methylation of these halosilane derivatives afforded C-methylated 1,1-dimethyl-1-silacyclohexanes. Free radical chlorination and bromination of these methylsilane derivatives gave the corresponding halomethylsilanes with retention of configuration. These stereospecific reactions converted Si-Cl derivatives from a mixture in which one of the two isomers predominated into a mixture in which the other isomer predominated. Fluorination of chloro- and bromosilane; derivatives afforded the corresponding fluoromethylsilanes, inversion of stereochemistry was observed. The reaction of C-methylated 1-methyl-1-phenyl-1-silacyclo-hexanes with bromine in carbon tetrachloride gave C-methylated 1-bromo-1-methyl-1-silacyclohexane with inversion of stereochemistry. These bromosilanes isomerized to an equilibrium mixture in the presence of an excess of bromine. The conformational energies of C-methylated 1-methyl-1-silacyclohexane were studied by using MM2 force field calculations. The cis/trans isomerization of these methylsilane derivatives catalyzed by a small amount of nucleophilic reagent such as NH(,4)HF(,2) and CsF was also studied. The experimentally determined equilibrium mixture was comparable to that calculated by the force field method, and also agreed with the results obtained from the direct cyclization. The ring enlargements of five-membered ring silacyclopentanes containing an exocyclic chloromethyl group on silicon to a six-membered ring silacyclohexane in the presence of a nucleophilic reagent such as fluoride anion, or under thermolysis condition were investigated. The carbon center which migrates from silicon to the alpha-carbon in the ring enlargement is the secondary rather than the primary carbon center.

Pages

259

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