Catecholic motifs are present in numerous natural products and synthetic compounds used in various sectors of the chemical industries such as food, cosmetic, pharmaceutical and polymer industries. The antioxidant activity usually conferred to compounds bearing catecholic motifs is the property on which their application is often based. Although several (bio) chemical methods are available to chemists to produce catechols, the oxygenation of phenols constitutes one of the most practical approaches as long as the orthoselectivity of the process can be controlled. In this context, oxygenating hypervalent iodine(V) reagents offer a convenient metal-free solution. Among these reagents, 2-iodoxybenzoic acid (IBX) or its stabilized (non explosive) SIBX and polymer-supported versions have found the most useful and successful applications in the conversion of phenols into ortho-quinones, followed by reduction into catechols. Examples of oxygenative demethylation of 2-methoxyphenols and ortho-hydroxylation of phenolic compounds for the synthesis of biologically and industrially-relevant catechols are highlighted in this review article, together with some mechanistic discussions on these transformations.
Keywords: Ortho-hydroxylation, Ortho-quinones, catechols, hypervalent iodine(V) reagents, Iodylarenes, 2-Iodoxybenzoic acid (IBX), stabilized 2-Iodoxybenzoic acid (SIBX), polymer-supported IBX, ortho-oxygenations, catecholic