Protection of Alcohols

Alcohols are acids so they are typically not copatibile with very basic reagents including Grignard reagents, Organo sodium/lithum and LiAlH₄ (LAH).  Thus chemists have devised methods of protecting alcohols.  One method we will discuss here is to make Silyl ethers of alcohols using TMSCl.

The Silyl ether of an alcohol can be prepared as follows.  

Silyl ethers are easily hydrolyzed back to the corresponding alcohols under acidic conditions.

As an example suppose you would like to do an addition of a Grignard reagent to an α-hydroxyketone (red curved arrow below).  Unfortunately the Grignard reagent would undergo an acid/base reaction instead, deprotonating the hydroxyl group (green curved arrow)

This can easily be solved by protecting the alcohol before performing the Grignard addition.