Acetal Protecting Groups

Because the acetal functional group is tolerant to very basic and harsh conditions, forming acetals is a good way to protect an aldehyde or ketone.

For example, suppose you wish to prepare the following alcohol from a β-ketoester.

If you attempt to add the Girgnard reagent directly to the β-ketoester, the ketone will react as well.

One solution is to protect the ketone as an acetal before performing the Grignard addition.

Once the Grignard addition is completed, the final acidic workup (H₃O⁺) hydrolyzed the acetal back to the ketone.