Editorial: New Hypervalent Iodine Reagents for Oxidative Coupling

Abstract

In theory, oxidative coupling is a straightforward method for reducing the number of synthetic steps, avoiding the preparation of pre-activated substrates and less waste co-product generation by using metal salts. However, attempts at oxidative cross-coupling are challenging due to its limited synthetic applications and chemoselective issues. In recent years new oxidative coupling methods have emerged, using the C–H bond of the two substrates, and enabling the selective formation of cross-coupling products (Stuart and Fagnou, 2007). One of the innovative research fronts in this area to have emerged in the past decade is the advance of oxidative coupling chemistry that uses hypervalent iodine reagents (Kita and Dohi, 2015; Yoshimura and Zhdankin, 2016), especially catalytic utilizations (Dohi and Kita, 2009; Dohi et al., 2013; Ito et al., 2013). This Research Topic discusses recent advancements of oxidative couplings and related reactions using hypervalent iodine compounds, highlighting the versatility of these reagents and their continuous development. Contributing to the recent advances in this area, the Research Topic includes contributions by experts exploring designs, preparations, reactions, mechanistic studies of hypervalent iodine compounds, and cooperative reaction systems with transition metals and photoredox catalysts, outlining how these synthetic applications can obtain useful organic molecules, such as pharmaceutical compounds. In recent years there have been a number of successes in the participation of hypervalent iodine compounds in transitionmetal chemistry, which serve as strong electrophiles and powerful oxidizing agents, especially for the palladium-catalyzed couplings. The review by Shetgaonkar and Singh narrates recent advancements in this area, summarizing extensive work in the field of Pd-catalyzed C–H functionalizations, arylations, and other miscellaneous transformations with hypervalent iodine reagents and diaryliodonium(III) salts. The synergistic combination of photoredox catalysis with hypervalent iodine reagents is one of many useful areas of organic synthesis. Chen et al. describe recent synthetic applications with visiblelight-induced photoredox catalysis, focusing on the photochemical roles of hypervalent iodine reagents. However, a wide range of hypervalent iodine compounds still need to be explored under these conditions to bring out more synthetically useful transformations. We anticipate an expansion of this hot research area in the next few years. In 2009, a novel cross-coupling method of heteroaromatic compounds was developed by exploiting the unique reactivities of diaryliodonium(III) salts (Kita et al., 2009). Since then, the chemistry of heteroaryliodonium(III) salts has undergone significant developments. They have Edited and reviewed by: Iwao Ojima, Stony Brook University, United States