Oxidation of Phenolic Compounds with Organohypervalent Iodine Reagents

Abstract

The oxidation of phenols is a key biochemical process in oxidative phosphorylation, and it is also important in numerous biosynthetic pathways. Controlled oxidative transformations of substituted phenols are found in many synthetic organic sequences. Accordingly, a large number of oxidizing agents for phenols have been developed. Useful reagents include Fremy's salt (KSO 3 ) 2 NO,and a wide variety of other redox metal‐based oxidants such as Pb(IV), Mn(III), Tl(III), Cu(II), and Fe(III). Recently, organohypervalent iodine reagents have emerged as particularly useful agents for oxidizing phenols. In the area of natural product synthesis, organohypervalent iodine reagents have been used extensively to effect oxidative intramolecular bicyclization and spirocyclization. The focus of this chapter is on synthetic applications. The chapter also covers formation and applications of phenolic iodonium ylides. The processes that occur during the oxidation of phenols with organohypervalent iodine reagents can be divided into two categories. The first category involves ligand exchange of the phenolic proton with the hypervalent iodine reagent to generate the O‐I(III) intermediate, which is subsequently transformed to various products, depending upon the reaction conditions. These transformations include oxidation of phenols to quinones and related compounds, formation of spirocyclic and oxygen heterocyclic compounds via oxidative intramolecular participation reactions, and intramolecular carbon‐carbon bond formation via phenolic oxidative coupling. All of these reactions are driven by the reduction of iodine(III) [or iodine(V)] to iodine(I) (iodobenzene). A second class of reactions that is discussed in this chapter includes formation of stable iodonium salts and ylides, which are important intermediates in organic synthesis. These reactions occur via carbon‐I(III) bond formation without loss of iodobenzene.

Chemistry of Polyvalent Iodine

“…Numerous reviews on specific classes of polyvalent iodine compounds and their synthetic applications have recently been published 18–61. Most notable are the specialized reviews on [hydroxy(tosyloxy)iodo]benzene,41 the chemistry and synthetic applications of iodonium salts,29,36,38,42,43,46,47,54,55 the chemistry of iodonium ylides,56–58 the chemistry of iminoiodanes,28 hypervalent iodine fluorides,27 electrophilic perfluoroalkylations,44 perfluoroorgano hypervalent iodine compounds,61 the chemistry of benziodoxoles,24,45 polymer-supported hypervalent iodine reagents,30 hypervalent iodine-mediated ring contraction reactions,21 application of hypervalent iodine in the synthesis of heterocycles,25,40 application of hypervalent iodine in the oxidation of phenolic compounds,32,34,50–53,60 oxidation of carbonyl compounds with organohypervalent iodine reagents,37 application of hypervalent iodine in (hetero)biaryl coupling reactions,31 phosphorolytic reactivity of o -iodosylcarboxylates,33 coordination of hypervalent iodine,19 transition metal catalyzed reactions of hypervalent iodine compounds,18 radical reactions of hypervalent iodine,35,39 stereoselective reactions of hypervalent iodine electrophiles,48 catalytic applications of organoiodine compounds,20,49 and synthetic applications of pentavalent iodine reagents 22,23,26,59…”

Dearomative dihydroxylation with arenophiles

“…Despite their strategic and widespread use, most dearomative strategies do not result in the introduction of additional functionality. Indeed, the venerable dissolving-metal reduction (Birch reduction) 13 , oxidative dearomatization of phenols 14 , and arene–alkene photocycloadditions 15 are exceptionally powerful synthetic transformations; however, most of the dearomatized products have to be subjected to further manipulations to install the desired level of functionalization. To date, only certain stoichiometric reactions of transition-metal complexes based on Os, Ru, Re, Cr and Mn can enable more elaborate functionalizations of the corresponding metal-bound arenes (Fig.…”

Asymmetric oxidative dearomatizations promoted by hypervalent iodine(III) reagents: an opportunity for rational catalyst design?

“…8 These two-electron oxidations involve the addition of a nucleophile to the aromatic ring of the phenol and result in the formation of either a 2,4-cyclohexadienone ( 1 ) or a 2,5-cyclohexadienone ( 2 ). Nucleophiles used in these conversions include: electron-rich arenes, 9 heteroatom-based nucleophiles, (e.g.…”