Aerobic Oxidative Functionalization of Indoles

Abstract

The synthetic methodology for direct indole functionalizations is of great significance in indole chemistry and has been intensively investigated in the last few decades. From the perspective of green chemistry, oxygen is the best choice as the terminal oxidant in molecular synthesis. Hence, aerobic oxidative functionalization of indoles became a hot research topic in the last decade. Numerous efficient protocols in this field have been discovered that enable facile and efficient transformations of indoles to related valuable compounds, which are summarized and discussed in detail in this review.

Oxidative Cleavage of Indoles Mediated by Urea Hydrogen Peroxide or H2O2 in Polar Solvents

“…Compounds bearing indole moieties are widely present in many naturally occurring compounds, mainly alkaloids, with most of them possessing biological activity [1] . Therefore, it is not surprising that several different strategies have been developed for their further elaboration and transformation [2] . Among them, the oxidative cleavage of C2−C3 double bond of indoles, known as Witkop oxidation, [3,4] gives access to a variety of 2‐ketoacetanilide derivatives, which are key intermediates in the synthesis of quinolones and related bioactive compounds.…”

Sulfenylation of Indoles Mediated by Iodine and Its Compounds

“…For the direct sulfenylation of indole ring [12] systems based on transition metals salts and strong bases are actively used [13] . During the last decades, organic reactions mediated by iodine and its compounds are getting a significant attention in scientific community [14] .…”

Recent Studies of Bifunctionalization of Simple Indoles

“…Besides, the molecular structures of well‐known drugs such as sumatriptan, tadalafil, fluvastatin and rizatriptan are based on indole frameworks [2e] . In 2020, Liu and co‐workers [1a] reviewed the oxygen‐mediated functionalization of indoles. Sandtorv [1c] and Djakovitch [1d] respectively summarized the transition metal‐catalyzed C‐H [1c,d] or N‐H [1d] activation of indoles.…”