I. Exploration of a synthetic route to endo-5-trimethylsilyl norborn-2-ene; II. Solvent effects in the tri-n-butyl tin hydride reduction of alkyl bromides; III. Hydroboration of (chloroethynyl)trimethylsilane
A project to unequivocally characterize both endo- and exo-5-trimethylsilylnorborn-2-ene was undertaken. A key intermediate in the proposed reaction sequence, endo-5-(dichlorosiloxy)norborn-2-ene, was prepared and characterized. The next step, an intramolecular hydro-silylation, proved to be impossible to effect under all reaction conditions tried, polymerization occurring instead. The spectral assignments of these endo- and exo-5-trimethylsilylnorborn-2-enes are therefore still in doubt. The reduction of alkyl halides with tin hydrides is known to be a free radical process. Inasmuch as free radical chlorination has been shown to be markedly affected by the solvent employed, this free radical reduction was investigated to see if selective reduction could be accomplished by varying the solvent in which it is carried out. There was no significant solvent effect noted in this series of reactions. As a reactant in other projects, synthetically useful quantities of cis-chlorovinyltrimethylsilane were desired. As preparations in the literature afford this in very minor amounts, another preparation sequence was attempted. This method involved preparation of (chloro-ethynyl)trimethylsilane followed by its reduction via hydroboration, a sequence known to produce cis-alkenes in high yields in all-carbon analogues. In the present system, however, dihydroboration resulted, yielding a mixture of products which contained insignificant amounts of the desired olefin.