Metal-free synthesis of aryl esters by coupling aryl carboxylic acids and aryl boronic acids

A facile synthesis of aryl esters is developed by coupling aryl carboxylic acids and aryl boronic acids in the presence of PhI(OAc)₂ and carbonyl diimidazole. A wide range of functional groups were tolerant to the metal-free reaction condition that led to the desired products in good yields.     

Microwave-assisted selenium dioxide oxidation of aryl methyl ketones to aryl glyoxals

We report an improved procedure for the synthesis of phenyl glyoxal and a series of para-substituted aryl glyoxals by microwave-assisted selenium dioxide oxidation. The reaction time has been reduced from several hours to three minutes for activated aryl methyl ketone substrates and 18 min for deactivated substrates, with all reactions affording quantitative conversion into the corresponding aryl glyoxals.     

Triorganotin aryl selenides

The SnSe bond in trimethyltin aryl selenides is cleaved on reaction with selenenyl halides, sulphenyl halides, alkyl halides and allyl halides. Thus Me₃SnSePh reacts with PhSeCl, 4-Me-2-NO₂C₆H₃SCl, RI (R = CH₃ or Ph₃SnCH₂) and CH₂CHCH₂Br to give PhSeSePh, 4-Me-2-NO₂C₆H₃SSePh, RSePh and CH₂CHCH₂SePh, respectively. The diselenide, PhSeSePh, is also obtained from Me₃SnSePh on reaction with either 4-MeC₆H₄SO₂Cl or NaIO₄. Exchange reactions also occur between Me₃SnSePh and Ph₃SnCl or PhHgCl.     

Electrophilic fluorination of aryl tin and aryl mercury derivatives

Cleavage of aryl-tin and aryl-mercury derivatives with CF₃OF occurs particularly readily and the mercury derivatives give the corresponding arylfluorine compounds in especially high yield.     

Iodination of aryl amines in a water-paste form via stable aryl diazonium tosylates

The diazotization of aryl amines at room temperature in paste form with NaNO₂, p-TsOH and a small amount of water, followed by treatment with KI provides a new, simple, and effective route for the preparation of various aryl iodides. The water-paste and strong acid-free reaction conditions are environmentally friendly and compatible with acid-sensitive functional groups.     

Copper-catalyzed cross-coupling of aryl iodides and aryl acetylenes using microwave heating

An efficient copper-catalyzed cross-coupling of aryl iodides with aryl acetylenes under microwave irradiation is described. The reaction proceeds under microwave heating with 10 mol % CuI and 2 equiv Cs₂CO₃ in 43-87% yields.     

Palladium-catalyzed deacetonative coupling of aryl propargylic alcohols with aryl chlorides in water

A highly efficient and green process for palladium-catalyzed deacetonative coupling of aryl propargylic alcohols with aryl chlorides has been developed. The reaction occurs smoothly in neat water with 2?mol% PdCl₂ as catalyst, and various synthetically useful functional groups, including ether, aldehyde, ketone, and heterocyclics, are well tolerated. Moreover, the reaction could proceed through a consecutive Sonogashira/deacetonative process using 2-methyl-3-butyn-2-ol and aryl chlorides as coupling partners, affording the symmetric alkynes in good yields.     

Polymers from aryl glycidyl ethers

High molecular weight, linear polyethers were prepared by polymerizing a series of ring-substituted phenyl glycidyl ethers by using the ferric chloride–propylene oxide and dibutylzinc–water catalyst systems. The α-naphthyl, β-naphthyl, p-phenylphenyl, the o-, m-, and p-methyl, and the o- and p-chlorophenyl polymers resemble the parent polymer in that they are readily crystallizable polyethers which have melting points above 170°C. The other substituted poly(phenyl glycidyl ethers), including the o- and p-isopropyl, p-tert-butyl, p-octyl, and 2,4,6-trichloro derivatives show much less tendency to crystallize and are lower melting. The x-ray and electron diffraction data established that poly(o-chlorophenyl glycidyl ether) crystallizes in an orthorhombic unit cell; data obtained in a parallel study of unsubstituted poly(phenyl glycidyl ether) did not allow assignment of a specific structure.     

Reaction of 3-oxodihydrothionaphthenes with aryl diazonium chlorides and aryl isothiocyanates

The reaction of 3-oxodihydrothionaphthenes with aryl diazonium chlorides gives 2-arylhydrazono-3-oxodihydrothionaphthenes. By oxidation of the latter with hydrogen peroxide in glacial acetic add, new 2-arylhydrazonodihydrothionaphthene-(3)-one-1, 1-dioxides are synthesized. Condensation of aryl isothiocyanates with 3-oxodihydrothionaphthenes in tetrahydrofuran gives 2-(arylthiocarbamyl)-3-oxodihydrothionaphthenes; cyclization of the latter with -bromoacetophene leads to the synthesis of 4-phenyl-3-aryl-2-(3 -oxodihydrothionaphthylidene-2)-⁴-thiazolines.     

Photolytic transformation of aryl benzobisoxazole and aryl benzobisthiazole compounds into carbon dioxide

Solid‐state aryl benzobisoxazole and aryl benzobisthiazole compounds photolyzed in the presence of O₂ undergo cleavage to produce benzobisoxazoles (or benzobisthiazoles), benzonitriles, and benzamides. A very high percentage of the carbon atoms in one of the two segments from chain cleavage are converted to CO₂. This very unusual observation has been carefully confirmed by gas chromatography/mass spectroscopy analysis of the gaseous components in the photolysis vessel before and after photolysis, labeling experiments, and the correlation of the mass reduction in photolyzed polymers and the amount of CO₂ that evolves. The rate of CO₂ generation is used to compare the relative photostability of aryl benzobisoxazole and aryl benzobisthiazole model compounds, films, and fibers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1868–1877, 2007     

Palladium-catalyzed Mizoroki-Heck reaction of allyl aryl ethers with aryl iodides using phosphine-free hydrazone ligands

Palladium-catalyzed Mizoroki-Heck reaction of allyl aryl ethers with aryl iodides gave aryl cinnamyl ethers using a catalytic amount of Pd(OAc)₂ in DMF at 50 °C with phosphine-free hydrazone as a ligand in good yields.     

Copper catalyzed aryl amidation between Nα-Fmoc-protected amino-acid azides and aryl boronic acids

Abstract

A simple and efficient method for the synthesis of aryl amides via oxidative copper-catalyzed coupling of commercially available aryl boronic acids and bench stable N^α-protected amino-acid azides is reported. The potential utility of this protocol is demonstrated through a survey of diversely substituted aryl boronic acids and several side-chain functionalized amino-acid azides, leading to the preparation of the desired amidated products in good to excellent yields. This amide synthesis is suitable for the preparation of amides (such as peptide aryl amides and sterically hindered amino acids) that are not or hardly accessible via classical approaches.     

Synthesis of aryl alkynyl carboxylic acids and aryl alkynes from propiolic acid and aryl halides by site selective coupling and decarboxylation

The coupling of propiolic acid with aryl iodides afforded the aryl alkynyl carboxylic acids and aryl alkynes in generally good yields. Aryl alkynyl carboxylic acids were obtained when the reaction was performed in the presence of Pd(PPh₃)₂Cl₂ (2.5 mol %), dppb (5.0 mol %) and DBU (5 equiv) at 50 °C. For the synthesis of the terminal aryl alkynes, the reaction was conducted in the presence of Pd(PPh₃)₂Cl₂ (2.5 mol %), dppb (5.0 mol %), DBU (5.0 equiv), and Cu(acac)₂ (10 mol %) at 25 °C for 5 h, and further reacted at 60 °C for 6 h.     

Synthesis of aryl α-keto esters via the rearrangement of aryl cyanohydrin carbonate esters

A facile synthesis of aryl α-keto esters is reported involving the rearrangement of aryl cyanohydrin carbonate esters induced by the α-carbanion to the nitrile group generated by LDA. However, under similar conditions, an o-benzyloxycyanohydrin carbonate ester rearranged via a domino reaction leading to 2-phenylbenzofuran-3-carboxylic acid.     

Palladium catalyzed atom-efficient cross-coupling reactions of triarylbismuths with aryl iodides and aryl triflates

The atom-efficient cross-coupling of triarylbismuths with aryl iodides or aryl triflates using catalytic Pd(OAc)₂/PPh₃ and K₃PO₄ as base in DMF at 90 °C to afford the corresponding functionalized biaryls in high yields is reported.     

Unusual redox play of Mo(V/IV) during oxidative aryl–aryl coupling

The oxidative treatment of a suitable 1,3-diarylpropene precursor by MoCl₅ causes a series of redox steps yielding a dimer of dibenzo[a,c]cycloheptene. After the oxidative aryl–aryl bond formation, a C,H activation occurs providing a tropylium intermediate. Upon aqueous workup the metal waste acts as reductive media generating the dimer in an almost quantitative manner. The oxidative generation of the tropylium species as well as the subsequent redox play by the metal waste is unique and unprecedented. The dimeric compound can be oxidatively cleaved and subsequently decarboxylated providing the key intermediate of a previous synthesis of metasequirin-B derivatives.     

A facile one-pot synthesis of alkyl aryl sulfides from aryl bromides

A convenient one-pot synthetic method for the formation of alkyl aryl sulfides from various alkyl halides and lithium aryl thiolates that are prepared in situ by direct halogen-lithium exchange is reported. In particular, the method overcomes many of the problems encountered in previous reports; it is very quick, catalyst-free, and does not involve use of unstable aryl thiols.     

New insights into the titanium-mediated enantioselective oxidation of fluorinated aryl benzyl sulfides and aryl phenacyl sulfides

A fruitful switch from tert-butyl to cumene hydroperoxide was able to overcome a difficulty arose in the enantioselective oxidation of fluorinated aryl benzyl sulfide with hydroperoxides in the presence of a titanium/(S, S)-hydrobenzoin catalyst. New experiments show the complementarity of the old and the new protocols and indicate unequivocally the right choice leading to the corresponding highly enantioenriched sulfoxides. Moreover, in a totally unexpected way, the new protocol was able to overcome another difficulty arose in another field of research, that is the enantioselective oxidation of a fluorinated aryl phenacyl sulfide. Also in this case, the complementarity of behavior is acting. Finally, this investigation gives new support to the attribution of configuration of sulfoxides with ECD techniques, but only if the protocol outlined in our past research was followed thoroughly.     

Syntheses of polyfluoroalkyl aryl ether

The reactions of methoxyphenol and dihydroxybenzene with hexafluoropropene were studied. Eight new compounds 2-9 were separated from the reaction mixture of catechol and hexafluoropropene. The formation of these products was explained through nucleophilic attack of the aryloxy anion on hexafluoropropene, followed by elimination and addition (Scheme 1). However, the reaction of resorcinol and hydroquinone with C₃F₄ only gave the simple addition products 10 and addition-elimination products Z, E-11, 12. All new compounds were characterized by ¹H and ¹⁹F NMR, IR, MS and elemental analyses. The ¹⁹F NMR of seven membered ring compounds 4 and 5 were discussed in detail.     

Kinetics and mechanism of the C-S coupling reactions of aryl Grignard reagents with aryl arenesulfonates

The kinetics of the C-S coupling of arylmagnesium bromides with phenyl tosylate has been studied in THF: toluene at 90°C. The reaction is first order in Grignard reagent and first order in phenyl tosylate. Kinetic data, Hammett relationship and activation parameters are consistent with a nucleophilic addition mechanism involving rate determining attack of carbanion to sulfonyl group followed by a fast phenoxide group leaving.