Recycling and Catalytic Approaches for the Development of a Rare-Metal-Free Synthetic Method Using Hypervalent Iodine Reagent

Abstract

Oxidation reactions consist of a number of important transformations in organic synthesis. However, in spite of their utility in both laboratory-and industrial-scale production, oxidations are among the most problematic processes regarding the factors of safety, environmental friendliness, operational simplicity, etc. As oxidants, hypervalent iodines, such as phenyliodine(III) diacetate (PIDA) and phenyliodine(III) bis(trifluoroacetate) (PIFA), are among promising reagents for developing environmentally benign oxidation reactions due to their low toxicities, mild reactivity, ready availability, high stability, and easy handling. Our research objective is, largely in consideration of economic and environmental viewpoints, to enhance the synthetic values of these reagents as useful alternatives to highly toxic heavy-metal oxidants and even rare transition metals by pioneering their efficient utilization methods and unique reactivities. During this study, we have succeeded in the development of new recyclable reagents 1 and their catalytic utilization, and the design of a new chiral reagent 2 and its application to perform asymmetric oxidations. Accordingly, the recycling and catalytic use of a hypervalent iodine reagent became possible in many representative types of oxidative bond-forming reactions, some of which even include key transformations for natural product synthesis. A summary of these important achievements in hypervalent iodine chemistry are described in this review.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

“…While chemical reactions catalyzed by iodine species have been discovered only in 2005, the electrochemical generation of iodine­(III) species in situ from catalytic amounts of iodoarenes and the use of these species as the in-cell mediators in electrochemical fluorination reactions have been reported by Fuchigami and co-workers much earlier, in 1994 . The hypervalent iodine-catalyzed reactions have been discussed in several recent review articles. ,,− ,− ,− …”

A cost-effective extracorporeal magnetically-levitated centrifugal blood pump employing a disposable magnet-free impeller

“…Since these rare metals are only produced in a limited number of countries, the supply of rare-metal-containing products could be easily controlled by the domestic strategies of those countries. Hence, research to investigate technologies for rare-metal recycling, and even the development of rare-metal-free technologies have recently been progressed in other fields [8].…”

Speedy and Clean Hypervalent Iodine/Nitroxyl Radical Mediated Oxidation of Alcohols Using Recyclable Adamantane Reagent with Highly Active 2-Azaadamantane-<i>N</i>-oxyl Organocatalyst

“…Furthermore, the reagent could be nearly quantitatively recovered after the reactions by utilizing the insolubility of the formed tetraiodide 1′ in a polar solvent, specifically, methanol. Based on these significant advantages, the adamantane reagent 1 would serve as a recyclable and greener alternative to conventionally-used hypervalent iodine reagents, and mediate many types of oxidation reactions with efficiencies similar to those of phenyliodine diacetate (PIDA), [29][30][31][32][33][34][35][36] while the workup for the recovery of the reagent usually requires three separate steps, that is, i) evaporation of the reaction solvent, ii) precipitation by adding methanol, and then iii) filtering.Hence, the procedure to recover the tetraiodide 1′ started with the removal of the dichloromethane solvent under reduced pressure by a rotary evaporator, and the tetraiodide 1′ should be then precipitated by adding methanol to the resulting residue. Aimed at realizing a more practical procedure for the hypervalent iodine/nitroxyl radical oxidation of alcohols, we have further designed a more simplified and faster system that can skip the above mentioned precipitation steps, i) and ii), which are reported in this paper (Chart 1).…”

“…Furthermore, the reagent could be nearly quantitatively recovered after the reactions by utilizing the insolubility of the formed tetraiodide 1′ in a polar solvent, specifically, methanol. Based on these significant advantages, the adamantane reagent 1 would serve as a recyclable and greener alternative to conventionally-used hypervalent iodine reagents, and mediate many types of oxidation reactions with efficiencies similar to those of phenyliodine diacetate (PIDA), [29][30][31][32][33][34][35][36] while the workup for the recovery of the reagent usually requires three separate steps, that is, i) evaporation of the reaction solvent, ii) precipitation by adding methanol, and then iii) filtering.…”