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 Chapter 17: Aldehydes and Ketones. Nucleophilic Addition to C=O 
Ch 17 contents

Protecting Groups

The overall transformation required is ester to primary alcohol.  This is a reduction of the ester, which requires LiAlH4, but that will reduce the ketone as well which we don't want. We can avoid this problem if we "change" the ketone to a different functional group first. Conceptually, this is like being able to put a cover (shown below) over the ketone while we do the reduction, then remove the cover.
cartoon of a protecting group
In reality, the "molecular cover" is a protecting group. In this example, we protect the ketone as an acetal (which is an ether and doesn't react with LiAlH4)

Then we can reduce the ester to the primary alcohol.

Finally we can remove the protecting group:

Overall, this gives us the complete scheme:

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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary