Arylboronic iodination

This preparation illustrates an efficient two-step process for the transformation of a cycloalkenone to the corresponding a-substituted derivative. The first step involves the installation of an a-iodo substituent by a process thought to involve nucleophilic addition of pyridine, iodine capture of the resulting enolate, and pyridine-promoted elimination of pyridine.5 The resulting vinyl iodides are superior to other vinyl halides as participants in a variety of transition-metal catalyzed coupling reactions, illustrated here by the Suzuki coupling with an arylboronic acid. Other coupling partners that... 

The first preparations of diaryliodonium salts have been reported in the 19th century, but refinements and improvements keep appearing to date. In most cases an iodoaryl species containing iodine(III) is coupled with an arene or a derivative of it in a typical electrophilic aromatic substitution. Lithiated, stannylated or silylated aryls and arylboronic acids or borates have been introduced recently in order to avoid harsh conditions and to improve yields. The iodoaryl species may be also formed in situ from arenes and iodine(III) reagents. 

A boron-iodine exchange between vinyl- and arylboronic acids or esters and hypervalent phenyliodanes gave vinyl-aquation (117)) and aryl(phenyl)iodonium salts (Equation (118)) with complete retention of configuration.556,557... 

The carbamate substituted DHP derivative 647 has been deprotonated with f-BuLi in THF at — 78 °C to give the vinyllithium 648950 (Scheme 169). This reagent has been functionalized with a variety of electrophiles in good yields. The iodinated derivative 649 (X = I) underwent Suzuki-Miyaura couplings with arylboronic acids to afford the corresponding a-arylated DHPs. 

In their studies towards the synthesis of lukianol A, Wong et al. observed the regioselective zp o-iodination of pyrrole 187 followed by Sonogashira coupling to give 189 in quantitative yield overall [109]. lodopyrrole 188 also undergoes Suzuki couplings with arylboronic acids. 

Mention may be made of the Suzuki coupling of aryl halides and arylboronic acids. In earlier days, TPPMS could be used to convert the brominated or iodinated aromatics nowadays, cheaper chlorinated aromatics and catalysts based on Pd/TPPTS are used in an aqueous procedure on a commercial scale [Eq. (2)] [5]. 

Olofsson and coworkers have developed several efficient one-pot syntheses of diaryliodonium salts [385-390], A general and universal procedure provides both symmetrical and unsymmetrical diaryliodonium triflates 272 from both electron-deficient and electron-rich arenes 271 and aryl iodides 270 using mCPBA as the oxidant and trifiic acid (Scheme 2.78) [385-387]. The electron-rich diaryliodonium tosylates are prepared similarly using toluenesulfonic acid instead of trifiic acid as the additive [387]. Symmetrical diaryliodonium triflates can be synthesized by a modified one-pot procedure from iodine, arenes, mCPBA and trifiic acid under similar conditions [374,375]. A similar procedure based on a one-pot reaction of arylboronic acids, aryl iodides, mCPBA and BF3 -Et20 has been used for regioselective synthesis of unsymmetrical diaryliodonium tetrafiuoroborates [388,389]. In a further improvement of this approach, a range of... 

Aryliodoninm salts, Aral X [50], and some other hypervalent aryliodonium compounds take a part in further important alternative cross-coupling reactions with arylboronic acids [51], aryltrifluoroborates [52], triarylbismuth(V) compounds [53], and diaryltellurium dichlorides [54] to afford biaryls in good to excellent yields. For example, hypervalent iodine compoimd 466, readily produced from 2-iodobenzoic acid, reacts with arylboronic acids in palladium-catalysed process in Suzuki-Miyaura-fashion to give the 2-arylbenzoic acids in high yields [51], Table 12. 

Types of reaction C-O bond formation Reaction conditions Aqueous H2O2, room temperature Synthetic strategy tpso-Hydroxylation of arylboronic acids Catalyst Molecular iodine... 

Keywords Arylboronic acids, aqueous hydrogen peroxide, iodine, room temperature, ipso hydroxylation, phenols... 

A mixture of arylboronic acid (1 1 mmol) and iodine (5 mol%) in 30% aqueous hydrogen peroxide (2 mL) was stirred in a reaction vessel at room temperature for 30-120 min. on completion of reaction (as monitored by TLC), the reaction mixture was diluted with water and extracted with diethyl ether. The organic layer was then washed with sodium thiosulfate solution, and dried over anhydrous sodium sulfate and filtered. The organic solvent was evaporated out under reduced pressure to furnish the crude phenolic product 2 (80-93% yield) which was purified by column chromatography on silica gel (ethyl acetate/hexane) followed by crystallization. Physical and spectral properties of all the products were found to be in close agreement with those reported for authentic samples. 

Gogoi, A., and Bora, U. (2012). An iodine-promoted, mild, and efficient method for the synthesis of phenols from arylboronic acids. Synlett., 23, 1079-1081. 

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