Turning the Light on Phenols: New Opportunities in Organic Synthesis

Phenols (I) are extremely relevant chemical functionalities in natural, synthetic and industrial chemistry. Their corresponding electron‐rich anions, namely phenolates (I), are characterized by interesting physicochemical properties that can be drastically altered upon light excitation. Specifically, phenolates (I) become strong reducing agents in the excited state and are able to generate reactive radicals from suitable precursors via single‐electron transfer processes. Thus, these species can photochemically trigger strategic bond‐forming reactions, including their direct aromatic C−H functionalization. Moreover, substituted phenolate anions can act as photocatalysts to enable synthetically useful organic transformations. An alternative mechanistic manifold is represented by the ability of phenolate derivatives I to form ground state electron donor‐acceptor (EDA) complexes with electron‐poor radical sources. These complementary scenarios have paved the way for the development of a wide range of relevant organic reactions. In this Minireview, we present the main examples of this research field, and give insight on emerging trends in phenols photocatalysis towards richer organic synthesis. Phenols in the spotlight: Phenol and its derivatives are key moieties in organic chemistry. Conventionally, they are prepared through thermal functionalization strategies that present several drawbacks. Recently, alternative photochemical approaches have been implemented that involves phenols both as light‐harvesting substrates or as photo‐redox catalysts. This Minireview summarizes the most relevant examples within this field, highlighting the great versatility of simple phenolic frameworks in organic synthesis.