Hydroboration-Oxidation A Stereospecific Anti-Markovnikov Hydration

HYDROBORATION-OXIDATION A STEREOSPECIFIC ANTI-MARKOVNIKOV HYDRATION 

So far in this chapter, we have seen two ways to add the elements of water to alkenes to give alcohols. This section presents a third method, which complements the other two synthetically by giving in a different regiochemical outcome. The process involves a reaction that lies mechanistically between hydrogenation and electrophilic addition hydro-boration of double bonds. The alkylboranes that result can be oxidized to alcohols. 

The boron-hydrogen bond adds across double bonds 

Borane, BH3, adds to double bonds without catalytic activation, a reaction called hydro-boration by its discoverer, H. C. Brown.  

Hydroboration is not only stereospeciflc (syn addition), it is also regioselective. LFnlike the electrophilic additions described previously, steric more than electronic factors primarily control the regioselectivity The boron binds to the less hindered (less substituted) carbon. The reactions of the trialkylboranes resulting from these hydroborations are of special interest to us, as the next section will explain. 

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