Pyrrole-aryl derivatives are important due to their unique biological activities in medicinal chemistry. We now report a new oxidative biaryl coupling for pyrroles and indoles toward various arenes using a hypervalent iodine reagent and an appropriate stabilizer for pyrrolyl iodonium intermediates. The reactions readily provide a variety of desired coupling products in good yields.

A simple and efficient synthesis of phenol biaryls by the cross-couplings of quinone monoacetals (QMAs) and phenols is reported. The Brønsted acid catalytic system in 1,1,1,3,3,3-hexafluoro-2-propanol was found to be particularly efficient for this transformation. This reaction can be extended to the synthesis of various phenol biaryls, including sterically hindered biaryls, with yields ranging from 58 to 90 % under mild reaction conditions and in a highly regiospecific manner.

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A simple and efficient synthesis of phenol biaryls by the cross‐couplings of quinone monoacetals (QMAs) and phenols is reported. The Brønsted acid catalytic system in 1,1,1,3,3,3‐hexafluoro‐2‐propanol was found to be particularly efficient for this transformation. This reaction can be extended to the synthesis of various phenol biaryls, including sterically hindered biaryls, with yields ranging from 58 to 90 % under mild reaction conditions and in a highly regiospecific manner.

The metal-free arylative coupling of carboxylic acids using iodosoarenes without the use of a catalyst and base, which is applicable to even a highly-polar molecule bearing multiple alcohol groups, is reported. The in situ preparation of the reactive diaryliodonium(III) carboxylates is the important key to this approach, and the introduction of the trimethoxybenzene auxiliary enables both the smooth salt formations and the selective aryl transfer events during the couplings.

The data in this article are related to research article ‘‘Efficient N -arylation of azole compounds utilizing selective aryl-transfer TMP-iodonium (III) reagents (Koseki et al., 2019). For the title compound, phenyl(2,4,6-trimethoxyphenyl)iodonium(III) acetate (Ph(TMP)IOAc), the single-crystal X-ray diffraction measurement together with NMR analysis, like also the method of synthesis and crystallization are presented. The X-ray structure analysis has revealed that the two types of geometries regarding the acetate anion attached to phenyl (TMP)iodonium (III) cation are found in the crystal states.

The facile and clean oxidative coupling reaction of pyrroles with azoles has been achieved using the recyclable hypervalent iodine(III) reagents having adamantane structures. These iodine(III) reagents could be recovered from the reaction mixtures by a simple solid-liquid separation, i.e., filtration, for reuse.Key words oxidative coupling; hypervalent iodine reagent; recycle; pyrrole; azole; C-N bond formationThe N-pyrrolyl azoles are important fragments in the molecules of biological systems or in many pharmaceuticals, insecticides, and functional materials, especially, fluorescent dyes. [1][2][3][4] In spite of this interest, the preparations of N-aryl azoles are severely restricted because the nitrogen heteroaromatics are sometimes not a good substrate to use in the traditional arylation methods such as the Ullmann coupling, [5][6][7][8][9][10][11] since the pyrrole-based metal and halide compounds are sometimes unstable. Katritzky et al. reported the synthesis of pyrrolyl-benzotriazoles by the Mannich condensation of o-phthalaldehyde and 2,5-dimethoxy-2,5-dihydrofuran with primary amines, 12) but this method was not effective for pyrroles, and the desired products were produced only in less than 10% yields. As a new approach, the oxidative C-H bond functionalization strategies of pyrroles [13][14][15][16][17][18][19][20][21][22] might be expected to be an attractive methodology for enabling rapid access to these molecules. Recently, we have developed a new hypervalent iodine-induced oxidative coupling of pyrroles at the N 1 -positions of the azoles. 23) In 2014, Chen and colleagues reported the oxidative coupling method of 1,2,3-triazoles with pyrroles using N-iodosuccinimide (NIS) as an oxidant, in which the reactions preferentially occurred at the N 2 -position of the 1,2,3-triazoles.24) However, these methods produced stoichiometric quantities of iodoarene or succinimide as a waste product after the reaction (Chart 1).Hypervalent iodine reagents have received much attention due to their mild oxidation abilities and low toxicity, easy handling, as alternatives to toxic heavy metal reagents. [25][26][27][28][29][30][31][32] For developing a new coupling for heteroaromatic compounds, we have been engaged in the study of the oxidative C-H bond arylations using hypervalent iodine reagents that utilize the new reactivities of the heteroaromatic iodonium intermediates. [33][34][35][36][37] As mentioned, we developed a hypervalent iodineinduced oxidative coupling of pyrroles at the N 1 -positions of the azoles.23) This new method is versatile in allowing the reactions under metal-free and mild conditions, and tolerates a diverse series of functionalities of the pyrroles and azole coupling partners. We envisioned that a recycling version of this oxidative coupling should become feasible and provide an eco-friendly synthetic method (Chart 2) because a number of recent studies have demonstrated the utility of the recyclable hypervalent iodine reagents. 38-40) Results and DiscussionThe use of recyclable hypervalent ...

High reactivity of trimethoxyphenyl (TMP)iodonium(III) acetate for phenol O-arylation was achieved. It was first determined that the TMP ligand and acetate anion cooperatively enhance the electrophilic reactivity toward phenol oxygen atoms. The proposed method provides access to various diaryl ethers in significantly higher yields than the previously reported techniques. Various functional groups, including aliphatic alcohol, boronic ester, and sterically hindered groups, were tolerated during O-arylation, verifying the applicability of this ligand-and counterion-assisted strategy.