Hydroboration

The development of this technology and the underlying concepts were recognized by the Nobel Prize in Chemistry to Herbert C.

[7] In terms of synthetic results, diborane or the more conveniently handle BMS and borane-THF are equivalent.

In terms of regiochemistry, hydroboration is typically anti-Markovnikov, i.e. the hydrogen adds to the most substituted carbon of the double bond.

Hydroboration proceeds via a four-membered transition state: the hydrogen and the boron atoms added on the same face of the double bond.

However, an analysis of the orbitals involved reveals that the reaction is 'pseudopericyclic' and not subject to the Woodward–Hoffmann rules for pericyclic reactivity.

[8] Hydroboration of 1,2-disubstituted alkenes, such as a cis or trans olefin, produces generally a mixture of the two organoboranes of comparable amounts, even if the steric properties of the substituents are very different.

[9] As honored by the Nobel Prize to Brown, hydroboration is widely practiced because the alkylboranes are susceptible to many reactions.

Treatment of alkylboranes with base and hydrogen peroxide gives alcohols: The net reaction is hydration.

Because the addition of H-B to olefins is stereospecific, this oxidation reaction will be diastereoselective when the alkene is trisubstituted.

Hydroboration can also lead to amines by treating the intermediate organoboranes with monochloramine or O-hydroxylaminesulfonic acid (HSA).

[13] Such reactions have not however proven very popular, because succinimide based reagents such as NIS and NBS are more versatile and do not require rigorous conditions as do organoboranes.

When the addition of CO is conducted in the presence of a hydride reducing agent, the primary alcohol is produced.