12.13 : アルデヒドとケトンの保護基: はじめに

The carbonyl functional group in different compounds like aldehydes, ketones, esters, acids, and acid chlorides can be reduced to the hydroxyl group to give corresponding alcohols.

However, what happens if a compound has multiple reducible functional groups and selective reduction of one group over the other is desired?

While reducing a polyfunctional compound, for instance, a compound containing an ester and a ketone, the more reactive ketone gets preferentially reduced to an alcohol.

Consequently, selective reduction of the ester becomes difficult to accomplish in a single step.

The selective transformation of ester to alcohol can be achieved by protecting the more reactive ketone carbonyl group, then reducing the ester, and, finally, removing the protecting group to regenerate the ketone.

This selective protection is similar to protecting a car's windows with tapes to prevent them from getting painted when spray-painting a car's body.

Acetals and thioacetals are the preferred protecting groups for aldehydes and ketones because they can be easily formed and selectively removed under mild conditions, and they pull through several diverse reaction conditions.