Palladium-catalysed arylation of acetoacetate esters to yield 2-arylacetic acid esters

The coupling reaction between ethyl acetoacetate and a number of aryl halides in the presence of palladium acetate, a bulky and electron rich phosphine and K₃PO₄ is described. The arylated acetoacetate ester is de-acylated under the reaction conditions resulting in the generation of 2-arylacetic acid esters, constituting a mild alternative to direct arylation of carboxylate esters.     

Reactions of [(Me3Si)3CAlMe2] with substituted benzoic acids. Isolation of a rare organoalumoxane carboxylate

The reactivity of bulky tris(trimethylsilyl)methyl group substituted aluminum trialkyl [(Me₃Si)₃CAlMe₂·THF] (1) with a series of substituted benzoic acid derivatives has been investigated. An equimolar reaction of 4-methyl benzoic acid or 4-tert-butyl benzoic acid with 1 in toluene at 50 °C leads to the formation of cyclic dimeric aluminum carboxylates [(Me₃Si)₃CAl(Me)(μ-O₂CC₆H₄R)]₂ (R = Me 2; ^tBu 3). Reaction of 3,5-di-iso-propylsalicylic acid (H₂dipsa) with 1 leads to the exclusive isolation of a trimeric organoaluminum carboxylate [(Me₃Si)₃CAl(μ-dipsa)]₃ (4), in which each aluminum is bound to two carboxylates, a phenoxide, and an alkyl group and produce a 12-membered macrocycle. Deliberate, but controlled, introduction of water in the form of 3,5-di-tert-butyl salicylic acid monohydrate (H₂dtbsa·H₂O) in the reaction with 1 in toluene leads to the isolation of carboxylate [(Me₃Si)₃CAl(μ-O)(μ-Hdtbsa)}₂] (5) with a bicyclic structure. Compound 5 represents a rare example of an organoalumoxane carboxylate that simultaneously possesses alkyl, oxo, and carboxylate moieties on aluminum.     

Concise and diastereoselective approach to syn- and anti-N-tosyl-α-hydroxy β-amino acid derivatives

The methyl diazoacetate and aryl (N-tosyl)imines can be transformed into syn or anti α-hydroxy β-amino esters with high diastereoselectivities in three steps: the base promoted nucleophilic condensation of the methyl diazoacetate and aryl (N-tosyl)imines to give β-(N-tosyl)amino α-diazoesters, followed by oxidation with Oxone^® to generate α-oxo esters, which were reduced with NaBH₄ to yield the anti-N-tosyl-α-hydroxy β-amino ester, or hydrogenated with Pd/C (10%) as the catalyst to yield corresponding syn isomer, both in high diastereoselectivity.     

Silica supported perchloric acid (HClO4-SiO2): an efficient and recyclable heterogeneous catalyst for the one-pot synthesis of amidoalkyl naphthols

An efficient and direct protocol for the preparation of amidoalkyl naphthols employing a multi-component and one-pot condensation reaction of 2-naphthol, aromatic aldehydes, and acetonitrile or acetamide in the presence of silica supported perchloric acid under solvent, solvent-free, and microwave irradiation conditions is described. The present protocol with HClO₄-SiO₂ catalyst is superior to the recently reported catalytic methods. It is noteworthy that 1-amidomethyl-2-naphthols can be converted into important ‘drug like’ 1-aminomethyl-2-naphthol derivatives by amide hydrolysis.     

Suzuki Coupling of Cyclopropylboronic Acid With Aryl Halides Catalyzed by a Palladium–Tetraphosphine Complex

The tetraphosphine all‐cis‐1,2,3,4‐tetrakis(diphenylphosphinomethyl)cyclopentane (Tedicyp) in combination with [Pd(C₃H₅)Cl]₂ affords a very efficient catalyst for the coupling of cyclopropylboronic acid with aryl bromides and aryl chlorides. Higher reactions rates were observed with aryl bromides than with aryl chlorides; however, even in the presence of 1–0.4% of catalyst, a few aryl chlorides gave the coupling products in good yields. A wide variety of substituents such as alkyl, methoxy, trifluoromethyl, acetyl, benzoyl, formyl, carboxylate, nitro, and nitrile on the aryl halides are tolerated. The coupling reaction of sterically very congested aryl bromides such as bromomesitylene or 2,4,6‐triisopropylbromobenzene also proceeds in good yields.     

RuH2(CO)(PPh3)3-catalyzed arylation of aromatic esters using arylboronates via C-H bond cleavages

The RuH₂(CO)(PPh₃)₃-catalyzed C-H functionalization of aromatic esters with 5,5-dimethyl-2-aryl-[1,3,2]dioxaborinanes (arylboronates) gave the ortho arylation products. This coupling reaction can be performed with various combinations of isopropyl benzoate derivatives and arylboronates. Introduction of CF₃ group in the aromatic ring increased the reactivity of the esters. Pinacolone effectively served as an acceptor of a hydride generated by C-H bond cleavage, and the amount of pinacolone used also affected the yield of the arylation product.     

Microwave-promoted aminocarbonylation of aryl triflates using Mo(CO)6 as a solid CO source

Palladium-catalyzed carbonylations of aryl triflates with a range of nucleophiles using Mo(CO)₆ as a solid CO source were explored. The reactions proceeded smoothly providing moderate to good yields of the corresponding aryl amides, esters, or acylsulfonamides after only 20 min of microwave irradiation. The acyl transfer reagent 4-dimethylaminopyridine was found to promote some of the more difficult transformations.     

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.     

SmI2-Mediated 3-exo-trig cyclisation of δ-oxo-α,β-unsaturated esters to cyclopropanols and derivatives

In the presence of samarium diiodide and a proton source, δ-oxo-γ,γ-disubstituted-α,β-unsaturated esters of general formula R-CO-C(R′,R′)-CHCH-CO₂Bn readily cyclise to trans-cyclopropanol products and/or lactones derived from the cis isomers. For R=aryl, good stereoselectivities (ca 90%) in favor of the alcohols are generally obtained while a mixture of alcohols and lactones is obtained with R=alkyl or H. For R=cyclopropyl, the lactone is exclusively obtained in more than 90% yield. A mechanistic rationalisation of these variations of diastereoselectivity is proposed.     

Sulfamic acid: a novel and efficient catalyst for the synthesis of aryl-14H-dibenzo[a.j]xanthenes under conventional heating and microwave irradiation

A simple and convenient procedure for the synthesis of aryl-14H-dibenzo[a.j]xanthenes is described through a one-pot condensation of β-naphthol with aryl aldehydes in the presence of sulfamic acid as the catalyst in a solvent-free media using both conventional heating and microwave irradiation.     

trans-Pd(OAc)2(Cy2NH)2 catalyzed Suzuki coupling reactions and its temperature-dependent activities toward aryl bromides

A new catalytic system based on Pd-simple amines for Suzuki coupling reactions of aryl bromides is described. A well-defined air-stable complex, trans-Pd(OAc)₂(Cy₂NH)₂ effectively promotes Suzuki couplings of aryl bromides with a range of aryl boronic acids to give diaryl products in high yields. It also exhibits temperature-dependent activity toward aryl bromides bearing different electronic substituents under reaction conditions.     

Triorganoantimony(V) carboxylates: Synthesis, characterization and crystal structure of [Me3Sb(O2C-C5H4N)2] · H2O

Reactions of [R₃Sb(OPrⁱ)₂] with N-heterocylic carboxylic acids gave compounds of the type [R₃Sb(O₂C-Ar)₂] (1) (R = Me, Et, Prⁱ, Ph; Ar = 2-C₅H₄N, 2-C₉H₆N). The mono-bromo compound [Me₃Sb(Br)(O₂C-C₅H₄N)] (2) exists in equilibrium with [Me₃Sb(O₂C-C₅H₄N)₂] and [Me₃SbBr₂]. All new compounds have been characterized by IR and NMR (¹H and ¹³C{¹H}) spectral data. X-ray structural analysis of one example, [Me₃Sb(O₂C-C₅H₄N)₂], isolated as its monohydrate, revealed an essentially trigonal bipyramidal geometry for the antimony atom defined by three equilaterally disposed methyl groups and two oxygen atoms from monodentate carboxylate groups, in apical positions. The crystal structure is consolidated into a three-dimensional network by cooperative O-H?O, O-H?N and C-H?O interactions.     

Preparation of methyl/benzyl(2-hydroxynaphthalen-1-yl)(aryl)methylcarbamate derivatives using magnesium hydrogen sulfate

A new approach to the synthesis of methyl/benzyl(2-hydroxynaphthalen-1-yl)(aryl)methylcarbamate derivatives based on the reaction of aldehydes, 2-naphthol and methyl/benzyl carbamate, using a catalytic amount of magnesium hydrogen sulfate [Mg(HSO₄)₂] as an efficient heterogeneous catalyst under solvent-free conditions has been developed.     

Pd2dba3/P(i-BuNCH2CH2)3N: a highly efficient catalyst for the one-pot synthesis of trans-4-N,N-diarylaminostilbenes and N,N-diarylaminostyrenes

A Pd₂dba₃/P(i-BuNCH₂CH₂)₃N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners.     

Efficient cleavage of carboxylic tert-butyl and 1-adamantyl esters, and N-Boc-amines using H2SO4 in CH2Cl2

A new procedure for the deprotection of carboxylic tert-butyl and 1-adamantyl esters, and N-Boc-amines using H₂SO₄ in CH₂Cl₂ is described. The proposed method is simple, cheap, eco-friendly and represents a valid alternative to existing ones, with special significance in large scale applications.     

On the catalytic duo PdCl2(PPh3)2/AuCl(PPh3) that cannot effect a Sonogashira-type reaction: a correction

In contrast to the observation made by the Laguna group, we report that the combination of PdCl₂(PPh₃)₂ and AuCl(PPh₃) makes a unique catalytic system that allows Sonogashira-type cross-coupling of both aryl and alkyl alkynes with aryl halides in excellent yields.     

Metal-free one-pot three-step process for the direct conversion of aryl alkynes into secondary amines with TfOH/B2(OH)4

A metal-free one-pot synthesis of secondary amines from aryl alkynes via hydration-condensation-reduction three-step process in the presence of TfOH and B₂(OH)₄ has been developed. A series of secondary amines were obtained with good functional group tolerance and satisfied yields.     

Reductive alkylation of perfluorocarboxylic acid esters with CCl3F or CCl4 and synthesis of higher linear perfluoroketones

Barbier-type reductive alkylation of perfluorocarboxylic acid esters (I) with CFCl₃ and activated Al was successfully performed to give α,α-dichloroperfluoroketones (II). A similar reaction of CF₃COOEt with CCl₄ and Al provided a convenient synthesis of CF₃COCCl₃. Ketones (II) were fluorinated further with SbF₅ to form higher linear perfluoroketones (IX). An alternative approach to the synthesis of ketones (IX) was proposed by reductive perfluoroalkylation of esters (I) under the action of R_FI and Al.     

An efficient FeCl3‐promoted O‐alkyl cleavage of esters to carboxylic acids

A reliable and practical procedure for FeCl₃‐promoted ester cleavage has been developed. Lewis acids including TiCl₄, ZnO and FeCl₃ etc. were investigated as promoters for O‐alkyl cleavage of carboxylic acid ester. Under optimal reaction conditions, FeCl₃ (1.5 equiv.) was found to possess the highest activity and efficiently enhanced dealkylation of aryl esters, alkyl esters and aromatic heterocyclic esters to give their corresponding carboxylic acids in 54–98% yield, the method provides a complementary access to dealkylation of ester under neutral condition. Copyright © 2011 John Wiley & Sons, Ltd.     

Pd2(dba)3/Xantphos-catalyzed cross-coupling of thiols and aryl bromides/triflates

The cross-coupling of aliphatic and aromatic thiols and aryl bromides/triflates mediated by a Pd₂(dba)₃/Xantphos catalytic system in refluxing xylene (140 °C) affords the corresponding aryl thioethers in good to excellent yields.