Question

Show the structures of the products you would obtain hydroboration-oxidation of the following alkenes:

a)

b)

Short answer

a)

b)

Step-by-step solution

Introduction

Hydroboration-oxidation is a process that produces alcohols, involving two steps. AntiMarkonikov’s rule is followed in which hydrogen from ${\mathrm{BH}}_3$attaches itself to the more substituted carbon and boron attaches to the least substituted carbon in alkene double bond. Boron accepts two electrons from electron rich alkene, in its empty p orbital. This Anti-Markonokov hydroboration mechanism is stereospecific (syn addition), in which the hydroboration takes place on the same face of the double bond leading to syn product.

Mechanism

This process begins with addition of borane ${\mathrm{BH}}_3$to the double bond which leads to the transfer of hydrogen atom to the carbon atom that is adjacent to the carbon atom bonded to boron. This step is repeated twice more until all the hydrogen atoms of BH3 are transferred to alkenes, giving three trialkyl borane. Therefore, a single mole of hydroborane can react with alkenes in a quantity of three moles. In the next step, the trialkylborane produced in the first step are treated with a base or water and hydrogen peroxide so that the boron-carbon bonds are replaced with C-OH group bond.

Reaction (a)

Reaction (b)