Chapter 12, Problem 12.15P

Interpretation Introduction

Interpretation:

The complete, detailed mechanism for alkoxymercuration part of the given reaction is to be drawn and the major product is to be predicted.

Concept introduction:

Oxymercuration-Reduction reaction is the addition of water to an alkene. In this reaction, an alkene is first treated with mercury (II) acetate, ${\text{Hg(OAc)}}_2$, in a water-THF solution, and that is followed by reduction with sodium borohydride. The product of oxymercuration-reduction is the one expected from Markovnikov’s rule, that is, the $\text{OH}$ group forms a bond to the carbon atom that can better stabilize a positive charge. Rearrangement does not take place with this reaction.

In step $\text{1}$, the $\text{Hg}$ atom is electron-deficient which is attacked by an electron-rich double bond in the alkene resulting in a three-membered mercurium ion intermediate.

In step $\text{2}$, the solvent, water-THF, acts as a nucleophile to open the ring.

In step $\text{3}$, the positively charged $\text{O}$ atom is deprotonated. The reduction is then carried out when ${\text{NaBH}}_{\text{4}}$ is added, in which $\text{Hg}$, containing the substituent, is replaced by $\text{H}$. In alkoxymercuration-reduction, the solvent system used is ethanol-THF instead of water-THF.

In the case of asymmetric alkene, alcohol attacks more highly substituted carbon to acquire more positive charge from $\text{Hg}$.