Non-Palladium-Catalyzed Oxidative Coupling Reactions Using Hypervalent Iodine Reagents

Abstract

Transition metal-catalyzed direct oxidative coupling reactions via C-H bond activation have emerged as a straightforward strategy for the construction of complex molecules in organic synthesis. The direct transformation of C-H bonds into carbon-carbon and carbon-heteroatom bonds renders the requirement of prefunctionalization of starting materials and, therefore, represents a more efficient alternative to the traditional cross-coupling reactions. The key to the unprecedented progress made in this area has been the identification of an appropriate oxidant that facilitates oxidation and provides heteroatom ligands at the metal center. In this context, hypervalent iodine compounds have evolved as mainstream reagents particularly because of their excellent oxidizing nature, high electrophilicity, and versatile reactivity. They are environmentally benign reagents, stable, non-toxic, and relatively cheaper than inorganic oxidants. For many years, palladium catalysis has dominated these oxidative coupling reactions, but eventually, other transition metal catalysts such as gold, copper, platinum, iron, etc. were found to be promising alternate catalysts for facilitating such reactions. This review article critically summarizes the recent developments in non-palladium-catalyzed oxidative coupling reactions mediated by hypervalent iodine (III) reagents with significant emphasis on understanding the mechanistic aspects in detail.

Keywords: catalyst; copper; gold; hypervalent iodine reagents; oxidant; oxidative coupling.

FIGURE 1

Hypervalent iodine (III)/(V) reagents 1–19.

FIGURE 2

Gold-catalyzed oxidative coupling of arenes 20 for the synthesis of biaryls 21 using PhI(OAc)₂ 3 as an oxidant.

FIGURE 3

Gold-catalyzed synthesis of biaryls 24 via oxidative coupling of pentafluorophenyl gold(I) complexes 22 with electron-rich arenes 23 using PhI(OAc)₂ 3 as an oxidant.

FIGURE 4

Gold-catalyzed C–H alkynylation of arenes/hetero-arenes using a benziodoxolone-derived hypervalent iodine reagent 14 as an acetylene transfer reagent.

FIGURE 5

Gold-catalyzed oxyarylation of mono- and gem-di-substituted olefins 39 using IBA 8 as an oxidant.

FIGURE 6

Au(II)-catalyzed α-C (sp³)–H acyloxylation of methyl sulfides 43 using bis(acyloxy)iodobenzene 44 as an oxidant.

FIGURE 7

Cu(II)-catalyzed C–H bond arylation of indoles 49 using diaryliodonium salts 15 as a coupling partner.

FIGURE 8

Cu(II)-catalyzed selective meta arylation of amides 57 using iodonium salts 15 as an arylating agent.

FIGURE 9

Copper-catalyzed C–H arylation of fused-pyrimidinone derivatives 61 using diaryliodonium triflates 15 as an aryl source.

FIGURE 10

Copper-catalyzed C–H/N−H arylation of indoles 49 with diaryliodonium salts 65 as an aryl source.

FIGURE 11

Copper-catalyzed intramolecular cyclization of N-substituted amidobiphenyls 66 using PhI(OAc)₂ 3 as an oxidant.

FIGURE 12

Copper-catalyzed synthesis of multi-heterocyclic compounds 72 from 6-anilinopurine nucleosides 71 using PIDA 3 as an oxidant.

FIGURE 13

Copper-catalyzed ring expansion of alkene-substituted cyclobutanol derivatives 76 using azidobenziodazolone 77 as an azide precursor.

FIGURE 14

Cu(I)-catalyzed allylic trifluoromethylation of inactivated terminal olefins 79 using Togni’s electrophilic trifluoromethylating reagent 9.

FIGURE 15

Pt(II)-catalyzed C3-acetoxylation of indoles 49 to afford C3-acetoxylated indoles 81 using PhI(OAc)₂ 3.

FIGURE 16

Pt(II)-catalyzed C−H arylation of arenes 82 with diaryliodonium salts 15.

FIGURE 17

Iron(II)-catalyzed carbodi- and trichloromethylation/cyclization of N-arylacrylamides 87 using diaryliodonium salt 15 as an oxidant.

FIGURE 18

Iridium-catalyzed three-component coupling of styrenes 94 with diaryliodonium salts 15 and heteroatom nucleophiles 95.

FIGURE 19

Iridium-catalyzed sp³ C–H bond arylation of ketoximes 99 and nitrogen-containing heterocycles 100 with diaryliodonium salts 15.

FIGURE 20

Iridium-catalyzed C–H arylation of arenes and olefins 103 using diaryliodonium salts 15 as an arylating agent.

FIGURE 21

Iridium-catalyzed C–H alkenylation of 2-vinylanilines 105 using alkenyl-3-iodanes 106 as an electrophilic alkene-transfer reagent.

FIGURE 22

Iridium-catalyzed C–H alkynylation of 2-(hetero)arylquinazolin-4-ones 108 using TIPS-EBX 14 as an alkynylating reagent.

FIGURE 23

Ni(II)-catalyzed C (sp³) –H arylation of aliphatic amides 116 using diaryliodonium salts 15 as an arylating agent.

FIGURE 24

Ru²⁺-catalyzed arylation of 2-arylpyridines 122 with Ar¹Ar²IOTf 15 as an arylation reagent.