Protection for Phenols and Catechols

In developing a synthesis of any phenol-containing product, protection is often mandatory to prevent reaction with oxidizing agents and electrophiles or reaction of the nucleophilic phenoxide ion with even mild alkylating and acylating agents. Ethers are the most widely used protective groups for phenols and in general they are more easily cleaved than the analogous ethers of simple alcohols. Esters are also important protective groups for phenols, but are not as stable to hydrolysis as the related alcohol derivatives. Catechols can be protected in the presence of phenols as cyclic acetals or ketals or cyclic esters. Aryl and alkyl trimethylsilyl ethers can often be cleaved by refluxing in aqueous methanol, an advantage for acid- or base-sensitive substrates. The N-isopropyl carbamate is prepared from the isocyanide and is cleaved by hydrolysis with NaOH. Cyclic carbonates have been used to a limited extent only to protect the catechol group in a polyhydroxybenzene.