Alkyl Halides and Triflates to Alkanes

Alkyl Halides and Triflates to Alkanes. The normal requirements for conversion of alkyl halides (and triflates) to alkanes using organosilicon hydrides are essentially the same as those needed for the reduction of the corresponding alcohols, namely, the substrates must generally be able to serve as precursors to 

Alkyl Halides. Commonly, reductions with liquid silanes and liquid alkyl halides do not require the use of a solvent.186 When the alkyl halide is a solid, either pentane186 or dichloromethane may be used as solvent.192 No significant difference in reactivities is observed between alkyl chloride and bromide substrates,186 but allyl halides are more reactive than 2-halopropanes, which, in turn, are more reactive than 1-halopropanes.190,146 

In contrast to the behavior of primary alcohols, which resist reduction by organosilicon hydrides even in the presence of very strong acids, primary halo alkanes, including methyl iodide and ethyl bromide,186 undergo reduction when treated with aluminum chloride and organosilicon hydrides.146,185,186 Slow addition of a catalytic amount of aluminum chloride to a nearly equimolar 

Polymeric hydrocarbon by-products accompany the products of the latter two reactions. The structures of the products are clear evidence of the occurrence of 1,2-alkyl shifts leading to more stable carbocationic intermediates.  

The use of a deuterium-labeled organosilicon hydride and location of the deuterium isotope in the reduced product shows that 1,2-hydride shifts also occur. Thus, reduction of 1-bromohexane with triethylsilane-A yields hexane with all of the deuterium at C2 (Eq. 51) similar treatment of cyclohexylmethyl bromide produces melhyIcyclohexane-1 -di (Eq. 52).186 

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