AntiMarkovnikovhydratio

AntiMarkovnikovhydratio refers to the addition of water across a carbon-carbon double bond in a way that the hydrogen atom adds to the more substituted carbon and the hydroxyl group adds to the less substituted carbon. This is the opposite of the regiochemistry predicted by Markovnikov's rule, which states that in the addition of a protic acid HX to an alkene, the hydrogen atom adds to the carbon atom with the greater number of hydrogen atoms.

Anti-Markovnikov hydration is typically achieved through a two-step process. The first step is hydroboration, where a borane reagent, such as BH3, adds to the alkene. This addition follows anti-Markovnikov regiochemistry, with the boron atom attaching to the less substituted carbon and the hydrogen atom attaching to the more substituted carbon. The boron-carbon bond is then oxidized, usually with hydrogen peroxide in basic conditions, replacing the boron with a hydroxyl group. This oxidation step proceeds with retention of stereochemistry at the carbon atom.

The overall result of anti-Markovnikov hydration is the formation of a primary or secondary alcohol, depending on the starting alkene, with the hydroxyl group located at the less substituted position of the original double bond. This contrasts with direct hydration using acid catalysts, which yields alcohols according to Markovnikov's rule. Anti-Markovnikov hydration is a valuable synthetic tool for producing specific alcohol isomers that are inaccessible through direct hydration methods.