Diaryliodonium(III) salts: Arylating agents

Abstract

(A) Nucleophilic Substitution Reaction: Alkyl-substituted malonates and a-keto esters could be efficiently arylated by diaryliodonium salts in the presence of base to give the corresponding aryl derivatives under mild conditions.1b The electron- rich aromatic ring was less reactive, and thus the electron-deficient aromatic ring selectively reacted in this reaction. (B) Arylation of Carboxylic Acids: An efficient arylation of carboxylic acids with diaryliodonium salts was developed, giving aryl esters in high yields within short reaction times.2d The transition-metal-free conditions were compatible with a range of functional groups, and a good chemoselectivity was observed with the unsymmetric diaryliodonium salt according to the interplay of the steric demand, ortho effect, and/or the electron deficiency of the aromatic rings. (C) Selective Fluorination Utilizing Heteroaromatic Iodonium Salts: Diaryliodonium salts containing the a-thienyl group as an electronrich heteroaromatic moiety proved to be potent precursors for the nucleophilic, regioselective no-carrier-added (nca) radiofluorination of various arenes.2f The fluorination of the thiophene ring would not occur at all, and the nucleophilic introduction of nca [18F]fluoride into electron-rich aromatic compounds was possible in one step. (D) Suzuki Coupling with Sodium Tetraphenylborate: The palladium chloride catalyzed Suzuki coupling reaction of sodium tetraphenylborate with diaryliodonium salts was achieved by microwave irradiation in water without using base.3a This convenient method for the rapid formation of aryl carbon-carbon bonds occurred in excellent yields. (E) Use in Heck Reaction: A fast and convenient base-free Heck reaction of acrylic acids and allyl alcohols with diaryliodonium salts was achieved in water by microwave irradiation, providing a simple method for the synthesis of trans-cinnamic acids and cinnamyl alcohols in good yields in a short reaction time.3b (F) Use as Benzyne Precursors: The treatment of (phenyl)[2-(trimethylsilyl)phenyl]iodonium triflates with tetrabutylammonium fluoride could be utilized for the high yields of benzyne adducts in the presence of a trapping agent such as furans.4 Especially, the high-yield reactions would indicate the quantitative generation of benzynes and their efficient capture by the furans. (G) Oxidative C-H Activation/C-C Bond Formation: A new palladium-catalyzed method involving C-H activation/C-C bond formation using diaryliodonium salts as arylating agents was recently reported.5a This transformation has been applied to a variety of arenes and benzylic substrates having different directing groups (pyridines, quinolines, oxazolidinones, and amides), and could proceed with high levels of regiocontrol. © Thieme Stuttgart · New York.