Hydroborointioksidaatio

Hydroborointioksidaatio is a two-step organic reaction that achieves the Markovnikov hydration of alkenes and alkynes. It involves the initial addition of a borane reagent across the double or triple bond, followed by oxidation of the resulting organoborane. This process results in the net addition of water across the pi system, with the hydroxyl group ending up on the more substituted carbon atom and the hydrogen atom on the less substituted carbon atom, following Markovnikov's rule.

The first step, hydroboration, typically employs borane (BH3) or a substituted borane such as 9-borabicyclo[3.3.1]nonane (9-BBN) or disiamylborane. Borane is electrophilic and reacts with the electron-rich alkene or alkyne. The addition is syn, meaning that both the boron and hydrogen atoms add to the same face of the pi system. The boron atom preferentially adds to the less substituted carbon due to steric and electronic factors, leading to regioselectivity.

The second step, oxidation, usually involves hydrogen peroxide (H2O2) in basic conditions. The peroxide oxidizes the carbon-boron bond to a carbon-oxygen bond, effectively replacing the boron atom with a hydroxyl group. This oxidation step also proceeds with retention of stereochemistry at the carbon center. The overall transformation is a versatile method for preparing alcohols from alkenes and alkynes with high regioselectivity and often good stereoselectivity. It avoids the carbocation rearrangements often encountered in acid-catalyzed hydration reactions.