Umpolung Strategy for Arene C−H Etherification Leading to Functionalized Chromanes Enabled by I(III) N ‐Ligated Hypervalent Iodine Reagents

Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7-8 years, between 2016 and 2024.

Direct C4 and C2 C-H Amination of Heteroarenes Using I(III) Reagents via a Cross Azine Coupling

Aminated nitrogen heterocycles are valuable motifs across numerous chemical industries, perhaps most notably in small molecule drug discovery. While numerous strategies for installing nitrogen atoms onto azaarenes exist, most require prefunctionalization and methods for direct C-H amination are almost entirely limited to position C2. Herein, we report a method for the direct C2 and C4 C-H amination of fused azaarenes via in situ activation with a bispyridine-ligated I(III) reagent, [(Py)2IPh]2OTf, or Py-HVI. Unlike commonly used N-oxide chemistry, the method requires no preoxidation of the azaarene and provides unprecedented direct access to C4 amination products. The resulting N-heterocyclic pyridinium salts can be isolated via simple trituration. The free amine can be liberated under mild Zincke aminolysis, or the amination and cleavage can be telescoped to a one-pot process. The scope of the method is broad; the conditions are mild and operationally simple, and the aminated products are produced in good to excellent yields. Computational studies provide insights into the mechanism of activation, which involves an unusual direct nucleophilic functionalization of an I(III) ligand, as well as a kinetic basis for the observed C2 and C4 amination products.

Copper-Catalyzed Intramolecular Aldehyde-Ketone Nucleophilic Additions for the Synthesis of Chromans Bearing a Tertiary Alcohol Motif

The synthesis of chroman-3-ol derivatives via intramolecular nucleophilic additions has been established. Aldehydes can be used as alkyl carbanion equivalents via reductive polarity reversal which is facilitated by a copper catalyst and N-heterocyclic carbene ligand under mild conditions. The key to success is the difference in reaction activity between aldehydes and ketones. Finally, this methodology also can be used to construct other cyclic structures containing tertiary alcohols including tetraline, cyclohexane, indan, and 9,10-dihydrophenanthrene.

Updates on hypervalent-iodine reagents in metal-free organic synthesis

Hypervalent iodine (HVI) chemistry is a rapidly growing subdomain of contemporary organic chemistry because of its enormous synthetic applications. The high nucleofugality of the phenyliodonio group (I+Ph) and their radical...