Iodine was discovered in 1811 by French chemist Bernard Courtois and it was named by J. L. Gay Lussac in 1813. Because
iodine is the largest, least electronegative and most polarisable of the common halogens, it is capable of forming stable polycoordinate
high-valent (with a value of up to 7, IF7) compounds. The most common polyvalent organic iodine compounds are
I(III) and I(V) species. Hypervalent iodine reagents were discovered a long time ago and (dichloroiodo)benzene was prepared
in 1886 as the first stable polyvalent organic iodine compound by a German chemist, C. Willgerodt [1]. This was rapidly followed
by the preparation of many others, including the most common reagents (diacetoxyiodo)benzene and iodosylbenzene in
1892 [2], 2-iodoxybenzoic acid (IBX) in 1893 [3], and the first examples of diaryliodonium salts reported by C. Hartmann and
V. Meyer in 1894 [4]. In 1914, Willgerodt also published a comprehensive book in this field [5]. Over the last couple of
decades, hypervalent iodine chemistry has evolved from being a mere curiosity to the most thriving field in organic synthesis
[6]. The key to the incredible advancements achieved in this field is the ability of these reagents to act as oxidants as well as
electrophilic reagents in various organic transformations. Over 100 reviews summarizing various aspects of hypervalent iodine
chemistry have been published since the year of 2000, and hundreds of research works utilizing hypervalent iodine reagents are
published every year. The continuous development of numerous new hypervalent iodine reagents and the discovery of catalytic
applications of organoiodine compounds are the most impressive modern achievements in the field of organoiodine chemistry.
The discovery of highly efficient, enantioselective molecular catalysts based on the unique iodine redox chemistry has supplemented
a new aspect to the field of hypervalent iodine chemistry and opened a major surge of research activity. Some of the
major contributors in this area are Stang, Moriarty, Kita, Prakash, Wirth, Zhdankin, Ishihara, Kitamura, Ochiai, Togni, Muñiz,
Olofsson, Quideau, Waser, etc.
This mini-thematic issue of ‘Mini-reviews in Organic Chemistry’ includes research papers covering key topics of modern
hypervalent iodine chemistry. Halogenated aryls, olefins and alkynes are highly relevant and synthetically useful building
blocks in several areas of the chemistry. Hypervalent iodine(III)-based reagents are extensively used in the oxidative introduction
of the full family of the halogens, such as fluorination, chlorination bromination and iodination of different arenes, heteroarenes,
alkenes and alkynes. Solorio-Alvarado et al. presented some of the most representative iodine(III)-based oxidative
protocols for the introduction of halogens to arenes, olefins, and alkynes. This oxidative approach for the functionalization of
aromatic derivatives, resulted generally in the fast, efficient, non-toxic and easy to handle reactions with the final introduction
of the fluorine, chlorine, bromine and iodine atom. The application of iodine(III) and iodine(V) reagents in various oxidative
rearrangement processes generates diverse array of molecules. Singh et al., in their manuscript, described several oxidative
rearrangements such as aryl or alkyl group migrations, Beckmann rearrangement, ring contractions and ring expansions employing
different hypervalent iodine reagents. They also emphasized the utility of these reagents for the dearomatization of phenols which is a
remarkable reaction to build various types of naturally occurring spirocyclic scaffolds. A significant exploration of chiral hypervalent
iodine reagents to develop stereoselective oxidative rearrangements is also presented. [18F]-labeled drugs and radioligands are
commonly used in Positron-Emission Tomography (PET) radiopharmaceuticals for both clinical and preclinical research. Various
methods for the introduction of [18F] into complex molecules through fluorination reactions have been reported. Kikushima
et al. explored recent advances in [18F]-fluorination utilizing aryliodonium(III) compounds through late-stage [18F]fluorination
and derivatization of 18F-labeled building blocks.
Regardless of the fact that there are continuous developments in this field, there are still many areas yet to be investigated.
Refereeing from the advantages of hypervalent organic iodine reagents, it seems certain that they will be further used in sophisticated
organic syntheses.