Recent advances in transition-metal-free arylation reactions involving hypervalent iodine salts

Abstract

Diaryliodonium salts have become widely recognized as arylating agents in the last two decades. Both, symmetrical and unsymmetrical forms of these salts serve as effective electrophilic arylating reagents in various organic syntheses. The use of diaryliodoniums in C-C and carbon-heteroatom bond formations, particularly under metal-free conditions, has further enhanced the popularity of these reagents. In this review, we concentrate on various arylation reactions involving carbon and other heteroatoms, encompassing rearrangement reactions in the absence of any metal catalyst, and summarize advancements made in the last five years.

Keywords: arylation reaction; diaryliodonium salts; electrophilic arylation reagent; metal-free arylation; rearrangement reaction.

Figure 1

Various structures of iodonium salts.

Scheme 1

Αrylation of α-fluoroacetoacetamides 5 to α-aryl-α-fluoroacetoacetamides 7 and α-fluoroacetamides 8 using diaryliodonium salts 6.

Scheme 2

Proposed mechanism for the arylation of α-fluoroacetoacetamides 5 to α-aryl-α-fluoroacetoacetamides 7 and α-fluoroacetamides 8.

Scheme 3

α-Arylation of α-nitro- and α-cyano derivatives of α-fluoroacetamides 9 employing unsymmetrical DAISs 6.

Scheme 4

Synthesis of α,α-difluoroketones 13 by reacting α,α-difluoro-β-keto acid esters 11 with aryl(TMP)iodonium tosylates 12.

Scheme 5

Coupling reaction of arynes generated by iodonium salts 6 and arynophiles 14 for the synthesis of tetrasubstituted arenes 15.

Scheme 6

Metal-free arylation of quinoxalines 17 and quinoxalinones 19 with DAISs 16.

Scheme 7

Transition-metal-free, C–C cross-coupling of 2-naphthols 21 to 1-arylnapthalen-2-ols 22 employing diaryliodonium salts 16 as the aryl source.

Scheme 8

Arylation of vinyl pinacol boronates 23 to trans-arylvinylboronates 24 in presence of hypervalent iodine salt 16.

Scheme 9

Light-induced selective arylation at C2 of quinoline N-oxides 25 and pyridine N-oxides 28 in the presence of 26.

Scheme 10

Plaussible mechanism for the light-induced selective arylation of N-heterobiaryls.

Scheme 11

Photoinduced arylation of heterocycles 31 with the help of diaryliodonium salts 16 activated through donor–acceptor complex formation.

Scheme 12

Arylation of MBH acetates 33 with DIPEA and DAIRs 16.

Scheme 13

Aryl sulfonylation of MBH acetates 33 with DABSO and diphenyliodonium triflates 16.

Scheme 14

Synthesis of oxindoles 37 from N-arylacrylamides 36 and diaryliodonium salts 26.

Scheme 15

Mechanically induced N-arylation of amines 38 using diaryliodonium salts 16.

Scheme 16

o-Fluorinated diaryliodonium salts 40-mediated diarylation of amines 38.

Scheme 17

Proposed mechanism for the diarylation of amines 38 using o-fluorinated diaryliodonium salts 40.

Scheme 18

Ring-opening difunctionalization of aliphatic cyclic amines 41.

Scheme 19

N-Arylation of amino acid esters 44 using hypervalent iodonium salts 45.

Scheme 20

Regioselective N-arylation of triazole derivatives 47 by hypervalent iodonium salts 48.

Scheme 21

Regioselective N-arylation of tetrazole derivatives 50 by hypervalent iodonium salt 51.

Scheme 22

Selective arylation at nitrogen and oxygen of pyridin-2-ones 53 by iodonium salts 16 depending on the base and solvent used.

Scheme 23

N-Arylation using oxygen-bridged acyclic diaryliodonium salt 56.

Scheme 24

The successive C(sp²)–C(sp²)/O–C(sp²) bond formation of naphthols 58.

Scheme 25

Synthesis of diarylethers 62 via in situ generation of hypervalent iodine salts.

Scheme 26

O-Arylated galactosides 64 by reacting protected galactosides 63 with hypervalent iodine salts 16 in the presence of base.

Scheme 27

Esterification of naproxen methyl ester 65 via formation and reaction of naproxen-containing diaryliodonium salt 67 with p-toluic acid.

Scheme 28

Etherification and esterification products 72 through gemfibrozil methyl ester-derived diaryliodonium salts 71.

Scheme 29

Synthesis of iodine containing meta-substituted biaryl ethers 74 by reacting phenols 61 and cyclic diaryliodonium salts 73.

Scheme 30

Plausible mechanism for the synthesis of meta-functionalized biaryl ethers 74.

Scheme 31

Intramolecular aryl migration of trifluoromethane sulfonate-substituted diaryliodonium salts 75.

Scheme 32

Synthesis of diaryl ethers 80 via site-selective aryl migration.

Scheme 33

Synthesis of O-arylated N-alkoxybenzamides 83 using aryl(trimethoxyphenyl)iodonium salts 82.

Scheme 34

Synthesis of aryl sulfides 85 from thiols 84 using diaryliodonium salts 16 in basic conditions.

Scheme 35

Base-promoted synthesis of diarylsulfoxides 87 via arylation of general sulfinates 86.

Scheme 36

Plausible mechanism for the arylation of sulfinates 86 via sulfenates A to give diaryl sulfoxides 87.

Scheme 37

S-Arylation reactions of aryl or heterocyclic thiols 88.

Scheme 38

Site-selective S-arylation reactions of cysteine thiol groups in 91 and 94 in the presence of diaryliodonium salts 92 and 95 as aryl source.

Scheme 39

The selective S-arylation of sulfenamides 97 using diphenyliodonium salts 98.

Scheme 40

Plausible mechanism for the synthesis of sulfilimines 99.

Scheme 41

Synthesis of S-arylxanthates 102 by reacting DAIS 101 with potassium alkyl xanthates 100.

Figure 2

Structured of the 8-membered and 4-membered heterotetramer I and II.

Scheme 42

S-Arylation by diaryliodonium cations 103 using KSCN (104) as a sulfur source.

Scheme 43

S-Arylation of phosphorothioate diesters 107 through the utilization of diaryliodonium salts 108.

Scheme 44

Transfer of the aryl group from the hypervalent iodonium salt 108 to phosphorothioate diester 107.

Scheme 45

Synthesis of diarylselenides 118 via diarylation of selenocyanate 115.

Scheme 46

Light-promoted arylation of tertiary phosphines 119 to quaternary phosphonium salts 121 using diaryliodonium salts 120.

Scheme 47

Arylation of aminophosphorus substrate 122 to synthesize phosphine oxides 123 using aryl(mesityl)iodonium salts 120.

Scheme 48

Reaction of diphenyliodonium triflate (16) with DMSO (124) via thia-Sommelet–Hauser rearrangement.

Scheme 49

Synthesis of biaryl compounds 132 by reacting diaryliodonium salts 131 with arylhydroxylamines 130 in the presence of a base.

Scheme 50

Synthesis of substituted indazoles 134 and 135 from N-hydroxyindazoles 133.