Late stage functionalization of heterocycles using hypervalent iodine(III) reagents

Late stage functionalization (LSF) through direct X-H manipulations (X = C, N) enable synthetic chemists to accelerate the diversification of natural products, agrochemicals and pharmaceuticals allowing rapid access to novel bioactive molecules without resorting to arduous de novo synthesis. LSF does not only allow to tap the hitherto unexplored chemical space but also renders the synthetic sequence more straight forward, atom-economic and cost-effective. In this regard, recent decade has witnessed the emergence of hypervalent iodine(III) reagents as a powerful synthetic tool owing to their easy availability, mild reaction conditions, remarkable oxidizing properties and high functional group tolerance. Iodine(III) reagents have received tremendous applications in the regio- and chemo-selective late-stage functionalization of a diverse variety of heterocycles through an exciting range of transformations, such as, oxidative amination, cross-dehydrogenative coupling (CDC), fluoroalkylation, azidation, halogenation and oxidation. The present review, classified according to the types of synthetic method involved, encompasses all these recent developments in the field of transition-metal-free iodine(III)-catalyzed/mediated direct functionalizations of heterocycles with representative examples and insightful mechanistic discussions.