Hydrogen abstraction from triethylsilane

The rate of decarboxylation of aroyloxy radicals is about 10 near room temperature. Decarboxylation of alkanoyloxy radicals is even faster. Thus only very rapid reactions can compete with decarboxylation. Hydrogen abstraction from very reactive hydrogen atom donors, such as triethylsilane, can compete with decarboxylation at moderate temperatures. 

A teehnique that is a convenient source of radieals for study by EPR involves photolysis of a mixture of di-t-butyl peroxide, triethylsilane, and the alkyl bromide corresponding to the radieal to be studied. Photolysis of the peroxide gives t-butoxy radieals, whieh selectively abstract hydrogen from the silane. This reactive silicon radieal in turn abstracts bromine, generating the alkyl radieal at a steady-state eoncentration suitable for EPR study. 

The low reactivity of alkyl and/or phenyl substituted organosilanes in reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols. The reaction mechanism is reported in Scheme 5 and shows that alkyl radicals abstract hydrogen from thiols and the resulting thiyl radical abstracts hydrogen from the silane. This procedure, which was coined polarity-reversal catalysis, has been applied to dehalogenation, deoxygenation, and desulfurization reactions.For example, 1-bromoadamantane is quantitatively reduced with 2 equiv of triethylsilane in the presence of a catalytic amount of ferf-dodecanethiol. 

Benzylic or allylic oxygen functions react with Lewis acids such as trifluoroacetic acid to generate allyl or benzylic cations which abstract a hydride from silanes such as triethylsilane 84 b to result in the removal of the oxygen function in a process which has been called ionic hydrogenation and which has been reviewed [34-38]. 

Direct reductive elimination of the hydroxyl group can be achieved readily only for tertiary and benzylic alcohols, which are especially liable to form carbocationic intermediates in acidic media. These intermediates are able to abstract hydrogen from such hydride donors as triethylsilane. This procedure, ionic hydrogenation, was elaborated into a preparatively useful protocol ... 

---