Four-co-ordinate Boron Compounds

Lithium triethylborohydride continues to be a useful synthetic reagent. It has been reported that this reagent in THF reduces the toluene-p-sulphonates of primary and secondary alcohols to the corresponding alkanes. The reduction is even applicable to tosylates of cycloalkanols, hindered alcohols, and polyhydroxy derivatives. The reaction of lithium triethylborohydride with elemental sulphur has been reported to form rapidly Li aS or Li aS a (depending upon the stoicheiometry), which can then be used to prepare sulphides, RaS, and disulphides, RaS a, in high yield. Similarly, the publication of a convenient 

Savelyanov and L. G. Ezhova, Zhur. priklad. Khim Leningrad), 1978, 51, 121. 

Savelj anov, V. A. Panova, and R. T. Savelyanova, Zhur, priklad. Khim. Leningrad), 

The reaction of potassium hydride in THF with trialkylboranes has been found to proceed smoothly at 25 °C to produce the corresponding potassium trialkylborohydrides. A very complete study concerning steric effects in the reaction of a series of trialkylboranes with lithium and sodium hydrides in THF has been carried out. Sodium hydride exhibited greater reactivity than lithium hydride and the reactivity of the organoboranes decreased drastically as the steric hindrance increased.  

The initial complex derived from the reaction of a-methoxyvinyl-lithium with trialkylboranes has been found to be stable at — 80 °C and can be iodinated to yield enol ethers. Warming induced alkyl group migration leading to a new alkenyldialkylmethoxyborate salt which, when oxidized, produced methyl ketones.  

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