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A number of organic transformations have been achieved using hypervalent iodine reagents under mild reaction conditions. The use of these reagents as chiral organocatalyst exhibited highly selective asymmetric reactions.

Abstract: : Organoselenium chemistry has developed as an important tool in the field of synthetic and medicinal chemistry. Various organoselenium reagents have been developed and used successfully to achieve different organic transformations such as the selenocyclizations, oxyselenenylations and selenoxide eliminations etc. Additionally, the potential of organoselenium reagents is not limited their use as stoichiometric reagents but they have successfully used as organocatalyst in number of synthetic transformations. Various organic and inorganic oxidants have been identified as terminal oxidants to regenerate the active catalytic specie. In this review article, the recent progress of organoselenium reagents in catalysis is being highlighted along with their asymmetric variants.

Hypervalent iodine compounds as environmentally friendly and relatively inexpensive reagents have properties similar to transition metals. They are employed as alternatives to transition metal catalysts in organic synthesis as mild, nontoxic, selective and recyclable catalytic reagents. Formation of C-N, C-O, C-S, C-F and C-C bonds can be seamlessly accomplished by hypervalent iodine catalysed oxidative functionalisations. The aim of this review is to highlight recent developments in the utilisation of iodine(III) and iodine(V) catalysts in the synthesis of a wide range of organic compounds including chiral catalysts for stereoselective synthesis. Polymer-, magnetic nanoparticle- and metal organic framework-supported hypervalent iodine catalysts are also described.

The chemistry of hypervalent iodine reagents has emerged as an astonishing field in synthetic organic chemistry owing to its easy availability and benign environmental features. Hypervalent iodine reagents are mostly employed as alternatives in various metal-catalyzed reactions since they show similar reactivity to the transition metals, are less toxic, and less expensive. These reagents are often used as oxidants as well as electrophilic reagents in a number of organic transformations, such as oxidative functionalization, alpha C-H bond functionalization of carbonyl compounds, rearrangements, and cyclization reactions. Furthermore, the application of iodine(III) and iodine(V) reagents in various oxidative rearrangement processes generating a diverse array of molecules have been well explored. In this mini-review, the recent developments in the area of oxidative rearrangements, using hypervalent iodine reagents, have been covered.

A simple yet innovative approach for the construction of multi-substituted allylbenzenes 14, 16 and 18 with ‘donor-acceptor’ functionalities has been delineated through base-mediated ring transformation of 6-aryl-2H-pyran-2-ones 13, 15 and 17 respectively with commercially available 5-hexen-2-one 11 as carbanion source. The reactions were carried out at room temperature without using any catalyst or organometallic reagents with excellent functional group tolerance. Moreover, the present method is possible alternate route to access allylbenzenes apart from usual metal-catalyzed cross-coupling reactions.

Hypervalent iodine reagents have been developed as highly valuable reagents in synthetic organic chemistry during the past few decades. These reagents have been identified as key replacements of various toxic heavy metals in organic synthesis. Various synthetically and biologically important scaffolds have been developed using hypervalent iodine reagents either in stoichiometric or catalytic amounts. In addition, hypervalent iodine reagents have been employed for the synthesis of spirocyclic scaffolds via dearomatization processes. In this review, various approaches for the synthesis of spirocyclic scaffolds using hypervalent iodine reagents are covered including their stereoselective synthesis. Additionally, the applications of these reagents in natural product synthesis are also covered.

A metal-free, ultrasound-assisted approach for the synthesis of highly functionalized 2-tetralones in high yields is described. The process involves ring transformation of 2H-pyran-2-ones with the spirocyclic ketone 1,4-cyclohexandione monoethylene ketal to yield spiro­cyclic ketals and subsequent acid-mediated hydrolysis. This protocol is free from any organometallic reagents, is economical and tolerates a wide range of functional groups.

Highly functionalized spirocyclic ketals were synthesized through asymmetric oxidative spirocyclization via carbanion-induced ring transformation of 2H-pyran-2-ones with 1,4-cyclohexandione monoethyleneketal under alkaline conditions. Further acidic-hydrolysis of obtained spirocyclic ketals yields highly substituted 2-tetralone in good yield. Computational analysis based on the DFT calculations and MD simulations has been performed in order to predict and understand global and local reactivity properties of newly synthesized derivatives. DFT calculations covered fundamental reactivity descriptors such as molecular electrostatic potential and average local ionization energies. Nitrogen atom and benzene rings have been recognized as the most important molecular sites from these aspects. Additionally, to predict whether studied compounds are stable towards the autoxidation mechanism, we have also studied the bond dissociation energies for hydrogen abstraction and identified the derivative which might form potentially genotoxic impurities. Interactions with water, including both global and local aspects, have been covered thanks to the MD simulations and calculations of interaction energies with water, counting of formed hydrogen interactions, and radial distribution functions. MD simulations were also used to identify which excipient could be used together with these compounds, and it has been established that the polyvinylpyrrolidone polymer could be highly compatible with these compounds, from the aspect of calculated solubility parameters.

An ultrasound-assisted rapid synthesis of meta-terphenyls 9 by the carbanion-induced ring transformation reaction of 6-aryl-5-methyl-2H-pyran-2-ones 7 with functionalized ketones 8 under basic conditions at room temperature has been delineated. The present method gives an easy access to functionally crowded m-terphenyls 9 with notable features including mild reaction condition, remarkable functional groups tolerance, shorter reaction time and high product yields.