The intramolecular aminofluorination of homoallylamine derivatives using a reagent system of PhI(OAc)2 and Py·HF in CH2Cl2 at room temperature for 5 h gave N-tosyl-3-fluoropyrrolidines in good to high yields. Furthermore, the catalytic aminofluorination was furnished by the reaction using p-iodotoluene as a catalyst in the presence of Py·HF as a fluorine source and mCPBA as a terminal oxidant.

The 1,4-benzdiyne equvalent, [2,5-bis(trimethylsilyl)-4-(trifyloxy)phenyl](phenyl)iodonium triflate, was prepared from sodium 2,4,5-trichlorophenoxide. The chemoselective generation of an aryne from the side of the phenyliodonio group was observed after treatment with a fluoride ion. Double cycloaddition of 1,4-benzdiyne with different arynophiles was conducted in one pot, giving bis-cycloadducts in high yields. Similarly, the 1,3-benzdiyne equivalent bearing phenyliodonio and triflate groups was prepared from sodium 2,3,6-trichlorophenoxide. The 1,3-benzdiyne equivalent also underwent the chemoselective stepwise generation of arynes and the double cycloaddition with different arynophiles. These hybrid benzdiyne equivalents provided the double cycloadducts in high yields and enabled the convenient one-pot procedure for synthesis of polycyclic aromatic compounds.

A strategy for desilylative acetoxylation of (trimethylsilyl)arenes has been developed in which (trimethylsilyl)arenes are converted into acetoxyarenes. The direct acetoxylation is performed in the presence of 5 mol % of Pd(OAc)2 and PhI(OCOCF3)2 (1.5 equiv) in AcOH at 80 °C for 17 h. The acetoxyarenes are obtained in good to high yields (67–98%). The synthetic utility is demonstrated with a one-pot transformation of (trimethylsilyl)arenes to phenols by successive acetoxylation and hydrolysis. Furthermore, desilylative acyloxylation of 2-(trimethylsilyl)naphthalene using several carboxylic acids has been conducted.

Fluorination of styrene derivatives with a reagent system composed of μ-oxo-bis[trifluoroacetato(phenyl)iodine] and a pyridine·HF complex gave the corresponding (2,2-difluoroethyl)arenes in good yields. Similarly, the reagent of PhI(OCOCF3)2 and the pyridine·HF complex acted as a fluorinating agent for styrene derivatives. The fluorination of styrene derivatives with the pyridine·HF complex underwent under catalytic conditions using 4-iodotoluene as a catalyst and m-CPBA as a terminal oxidant.

The direct fluorination reaction of acetophenone using iodosylarenes and TEA·5HF was conducted under mild conditions except for use of a HF reagent. The fluorination reaction was applied to acetophenone derivatives, acetonaphthones, benzyl phenyl ketone, propiophenone, butyrophenone, 1-indanone, and phenacyl chloride, giving selectively the corresponding α-fluoroketone derivatives in good yields.

Catalytic fluorination of 1,3-dicarbonyl compounds with aqueous hydrofluoric acid proceeded efficiently with the aid of iodoarene catalysts in the presence of m-CPBA as a terminal oxidant. o-Iodotoluene, o-iodoanisole, and o-ethyliodobenzene showed a high catalytic efficiency to give 2-fluoro-1,3-dicarbonyl compounds in good yields.

A practical and safe synthesis of 1,2-bis(trimethylsilyl)benzene from 1,2-dichlorobenzene and Me3SiCl was achieved by use of a hybrid metal of Mg and CuCl in the presence of LiCl in 1,3-dimethyl-2-imidazolidinone (DMI). This method does not require a toxic HMPA, provides a high yield of the product under mild conditions, and is also applied to synthesis of substituted 1,2-bis(trimethylsilyl)benzenes and poly(trimethylsilyl)benzenes.

Intramolecular hydroarylation of 4-benzofuranyl alkynoates using Pd(OAc)2 as catalyst took place selectively and efficiently, giving angular furocoumarin derivatives in high yields. The parent angelicin was obtained in 80% yield by this method. The starting 4-benzofuranyl alkynoates were easily accessible from readily available 4-hydroxybenzofurans and alkynoic acids.

Phenyl(trimethylsilylethynyl)iodonium and tert-butyldimethylsilylethynyl(phenyl)iodonium triflates were applied to alkynylation of benzotriazole. Treatment of the silylethynyliodonium triflates with the potassium salt of benzotriazole ion in tBuOH and CH2Cl2 gave 2-(trimethylsilylethynyl)-2H-1,2,3-benzotriazole and 2-(tert-butyldimethylsilylethynyl)-2H-1,2,3-benzotriazole in 74% and 76% yields, respectively. The regioisomers, 1-silylethynyl-1H-1,2,3-benzotriazole derivatives, were minor. In both cases of the silyl-substitued ethynyliodonium salts, novel regioselective alkynylation of benzotriazole at the 2 position was observed.

FeCl3/AgOTf-catalyzed hydroarylation of propiolic acid with electron-rich arenes such as mesitylene, tetramethylbenzene, and pentamethylbenzene in trifluoroacetic acid proceeded to give 3-arylpropenoic acids in moderate to high yields. The same reactions with anisole and 1,4-dimethoxybenzene afforded double hydroarylation products, 3,3-diarylpropionic acids.

Palladium complexes with bidentate phosphine ligands, Pd(dppe)(OAc)2 and Pd(dppm)(OAc)2, were found to be effective catalysts for reactions of simple arenes with ethyl propiolate, affording arylbutadiene derivatives selectively.

Coumarin and its derivatives occur widely in nature, particularly in plants; many of them show biological activity1, 2, 3, 4. To date, many procedures for coumarin synthesis have been extensively studied1, 2, 3, 4, including the Perkin reaction, the Knoevenagel reaction and the Pechmann–Duisberg reaction. The latter has been widely applied to the synthesis of coumarin derivatives5. However, there are still limitations, such as the requirement of harsh reaction conditions, the need for a stoichiometric amount of a condensing agent and the difficulty in obtaining the starting 2-hydroxybenzaldehyde derivatives.Recently reported coumarin synthesis reactions have focused on palladium-catalyzed reactions of phenols and their derivatives: intermolecular and intramolecular reactions of 2-iodophenol or its O-acyl derivatives in the presence of CO (refs. 6,7), intramolecular cyclizations of (2-hydroxyphenyl)alkenes or alkynes8, 9, reactions of phenols and ethyl propiolates10 and reactions of 2-iodophenol and alkynes in the presence of CO11. However, a Pd(0) species is the actual catalyst in these reactions. To accomplish a catalytic cycle, these reactions need iodides or triflates as substrates6, 7, 8, 9, 11 or formic acid to re-oxidize the Pd(0) species10.We found earlier that hydroarylations of alkynes by simple arenes proceed at room temperature using a Pd(OAc)2 catalyst in trifluoroacetic acid (TFA) to give aryl-substituted alkenes (Fig. 1)12. Furthermore, we found that PtCl2/AgOTf13 and K2PtCl4/AgOTf14 were effective catalysts for the hydroarylation of propiolic acids, affording the corresponding cinnamic acids selectively. The K2PtCl4/AgOTf catalyst was the most effective in application to the hydroarylation of propiolic acid with less reactive benzene.In the same way, we have demonstrated that the intramolecular hydroarylation of aryl propiolates provides coumarin derivatives in high yields (Fig. 2)15. This Pd(II)-catalyzed intramolecular reaction proceeds with high efficiency under mild conditions. In this reaction, however, the starting aryl propiolates must be prepared by the condensation of propiolic acids and phenols.We have developed a straightforward synthesis of coumarins from phenols and propiolic acids (Fig. 3)16. This method is much simpler and more convenient as it does not need aryl propiolates as a substrate but uses the starting materials of aryl propiolates directly. It also has the following advantages. (i) The reaction proceeds at room temperature and does not need any additives such as re-oxidizing agents, which are usually used for transition metal–catalyzed coupling reactions. (ii) The preparation does not require any special conditions such as an inert atmosphere and can be conducted under atmospheric conditions.Steps 1–3, 15 minStep 4, 15 minStep 5, 15 minStep 6, 48 hStep 7, 5 minStep 8, 30 minSteps 9–13, 2 hSteps 14 and 15, 1 hSteps 16–18, 3 hStep 19, 30 minStep 20, 30 minStep 21, 12 hStep 22, 1 hTroubleshooting advice can be found in Table 1.Mp 142–144 °C (recrystallized from CH2Cl2/hexane) 1H NMR (300 MHz, CDCl3) δ 6.05 (s, 2H, OCH2O), 6.24 (s, 1H, =CH), 6.83 (s, 1H, ArH), 6.89 (s, 1H, ArH), 7.39-7.42 (m, 2H, Ph), 7.49-7.53 (m, 3H, Ph). 13C NMR (75.5 Hz, CDCl3) δ 98.45, 102.31, 104.26, 112.09, 112.73, 128.16, 128.82, 129.53, 135.57, 144.75, 151.07, 151.24, 155.80, 161.08.

Palladium complexes with bidentate phosphine ligands, Pd(dppe)(OAc)2 and Pd(dppm)(OAc)2, were found to be effective catalysts for reactions of simple arenes with ethyl propiolate, affording arylbutadiene derivatives selectively.