This Research Topic is Volume II of a series. The previous volume can be found here:
New Hypervalent Iodine Reagents for Oxidative CouplingHypervalent iodine reagents have recently received much attention in organic synthesis, by virtue of their low toxicity, mild reactivity, ready availability, high stability, easy handling, ease of recovery and recyclability, etc. Extensive applications were found to mediate a wide array of bond-forming reactions, and a variety of reactions available for natural product syntheses have been reported based on the unique reactivities. Hypervalent iodine reagents are now extensively accepted as mild, safe, and economical alternatives to the highly toxic heavy-metal oxidizers, i.e., lead(IV), mercury(II), and thallium(III) reagents.
One of the innovative research fronts in this area, that has appeared in the past decade, is the advance of the oxidative coupling chemistry using hypervalent iodine reagents. These cross-coupling reactions, discovered by Japanese chemists in the twentieth century, can provide powerful tools for the construction of complex molecules in organic synthesis. In general, these cross-couplings using organometallic compounds (e.g., [M].[Zn], Negishi; [B], Suzuki, etc.) with organic halides in the presence of some transition metal catalysts, such as palladium complexes, have been used for the effective formation of new carbon-carbon bonds. Although the methods can afford target products in high yields and with good selectivity, these typically require the stoichiometric activated coupling substrates, that is, the metal- and halogen-functionalized organics, and thus produce metallic salts as waste and byproducts from the reactions. In addition, the preparation of pre-activated substrates often requires several synthetic operations.
In theory, the oxidative coupling is a straightforward route which can reduce the number of synthetic steps by avoiding the preparation of pre-activated substrates. Besides, this strategy involves less waste material generation regarding metal salts. Under such situations, new oxidative coupling methods that directly use the C–H bond of the two substrates, instead of organic halides and organometallic compounds, have emerged in recent years, enabling the selective formation of cross-coupling products.
We hope that this Research Topic would provide the recent advances and seminal guidelines for understanding the versatility of these reagents in oxidative coupling reactions, for promising their continuous development in the future.
The current Research Topic is to cover the recent advances in the oxidative coupling using hypervalent iodine reagents. Areas to be covered in this Research Topic may include, but are not limited to:
• Suggestion of new strategy for transformation of C-H bonds (e.g., dehydrogenative coupling, C-H functionalization, etc.)
• Development of new Reaction that can introduce multiple functionalities (e.g., alkene and alkyne difunctionalization, benzyne and heteroaryne transformations, etc.)
• Design of new reagent and catalyst for the oxidative coupling with product control (e.g., chemoselective reagent and catalyst, chiral reagent and catalyst, etc.)
• New intermediate for the oxidative coupling strategy (e.g., new carbon source, carbene and radical precursors, unique iodonium compound, etc.)
• Asymmetric oxidative coupling (e.g., dearomatization, alkene and alkyne functionalization, desymmetrization, etc.)
• Synthetic application of oxidative coupling products (e.g., bioactive compounds, organic materials, atropisomeric compounds, such as biaryls, arylamines, etc.)
By these contributions, hypervalent iodines will continue to make an impact in the 21st century as unique and efficient oxidative coupling agents.