Microwave-assisted nickel(II) acetylacetonate-catalyzed arylation of aldehydes with arylboronic acids

Applying sealed vessel microwave heating at 180 °C in toluene the arylation of aromatic and aliphatic aldehydes with arylboronic acids using 1-2 mol % of Ni(acac)₂ as a catalyst can be performed efficiently within 10-30 min providing the desired diarylmethanols or benzyl alcohols in good yields.     

Microwave-assisted cross-coupling of 3-chloro-2-pyrazolines and 3-chloro-1-phenyl-1,4,5,6-tetrahydropyridazine with aryl boronic acids

3-Chloro-1-phenyl-2-pyrazoline and 3-chloro-1-phenyl-1,4,5,6-tetrahydropyridazine were coupled with aryl boronic acids in good yields under microwave heating conditions (140 °C, 5 min).     

Microwave-promoted cross-coupling of acid chlorides with arylboronic acids: a convenient method for preparing aromatic ketones

Simple catalytic systems for cross-coupling reactions of acyl chlorides with arylboronic acids under microwave conditions were tested. Microwave irradiation facilitated the reaction course. Mild reaction conditions afford the symmetrical and unsymmetrical aryl ketones in reasonable to high yields within a short time. A wide range of substrates bearing an electron-donating or an electron-withdrawing substituent on aryl ring of acid chloride as well as on boronic acid were examined and high yields of ketones were produced.     

Divergent synthesis of arylated pyridin-2(1H)-one derivatives via metal-catalysed cross-coupling processes

1,5-Di(hetero)arylated-pyridin-2(1H)-one derivatives have been readily obtained in good yields starting from 2-fluoro-5-pyridylboronic acid. The sequence comprises three steps: (i) palladium-catalysed Suzuki-Miyaura reaction; (ii) base-catalysed hydrolysis; (iii) copper-catalysed C-N coupling. X-ray crystal structures are reported for selected pyridin-2(1H)-one derivatives. These compounds are of interest as new scaffolds for drug discovery.     

The stereospecific preparation of two perfluoro-1,3-butadiene synthons; (E)-1-trimethylsilyl-1,2,3,4,4-pentafluoro-1,3-butadiene and (E)-1-tributylstannyl-1,2,3,4,4-pentafluoro-1,3-butadiene

(E)-1-Trimethylsilyl-1,2,3,4,4-pentafluoro-1,3-butadiene (1) can be stereospecifically prepared by Pd(0)/CuI catalyzed cross-coupling of (Z)-1-tributylstannyl-1,2-difluoro-2-trimethylsilylethene with iodotrifluoroethene. The corresponding (E)-1-tributylstannyl-1,2,3,4,4-pentafluoro-1,3-butadiene can be prepared via the stereospecific conversion of 1 with Bu₃SnOSnBu₃/KF (catalysis) to the corresponding vinylstannane.     

Microwave-assisted Pd(OH)2-catalyzed direct C−H arylation of free-(NH2) adenines with aryl halides

A direct C−H arylation of free-(NH₂) adenines using Pd(OH)₂/C (Pearlman’s catalyst) and stoichiometric amount of copper iodide under ligandless microwave activation is described. This new protocol proved to be highly effective to synthesize a variety of 8-aryladenine derivatives 3 without prior protection of the amino substituent. The arylation reaction takes place rapidly within few minutes and allows the coupling to proceed regioselectively at the 8-position with a wide range of aryl halides including aryl iodides, bromides and the less reactive aryl chlorides.     

Use of a bulky phosphine of weak σ-donicity with palladium as a versatile and highly-active catalytic system: allylation and arylation coupling reactions at 10-10 mol% catalyst loadings of ferrocenyl bis(difurylphosphine)/Pd

Carbon-carbon(sp²-sp² and sp¹-sp²) and carbon-nitrogen (nucleophilic allylation) coupling processes are promoted by a catalytic system containing [PdCl(η³-C₃H₅)]₂ with the new ferrocenyl bis(difurylphosphine) 1,1′-bis[di(5-methyl-2-furyl)phosphino]ferrocene, Fc[P(Fu^Me)₂]₂. Starting from aryl bromides or allylic acetates this versatile catalyst system may be used at low palladium loadings (10⁻¹-10⁻⁴ mol%) in some Heck, Suzuki, Sonogashira and allylic amination reactions to give cross-coupled products in excellent yield. Remarkably high activity is obtained in allylic substitution reactions, providing a significant impetus for the development of bulky phosphines possessing weak σ-donicity for this particular reaction.     

Microwave-enhanced Pd(0)/acetic acid catalyzed allylation reactions of C, N, and O-pronucleophiles with alkynes

An efficient method for the allylation of C, N, and O-nucleophiles with alkynes under solvent-free conditions and by microwave activation is established. The process can be termed as a real eco-chemical process since no waste elements are produced in the reaction, moreover it is solvent free. This technique can also be used for the allylation of dimethyl methylmalonate, which proves inert under the previously reported reaction conditions (refluxing in 1,4-dioxane).     

Microwave-assisted synthesis of sterically hindered 3-(5-tetrazolyl)pyridines

Sterically hindered 2,4-disubstituted 3-(5-tetrazolyl)pyridines were efficiently prepared from the corresponding nicotinonitriles using microwave technology.     

Palladium catalysed regio- and stereoselective synthesis of (E)-4-aryl-1,3-bis(trimethylsilyl)but-3-en-1-ynes

A practical and general synthetic approach to a series of 4-aryl-but-3-en-1-ynes is described. In the presence of palladium complexes a variety of aryl bromides (or iodides) undergo coupling with two equivalents of trimethylsilylacetylene with the formation of (E)-4-aryl-1,3-bis(trimethylsilyl)but-3-en-1-ynes. The protocol is simple, efficient, and affords synthesis of regio- and stereoselectively target products in good to high yields.     

Stereoselective transformation of easily available (2Z,4E)-2,4-alkadien-1-ols into (E)-3-alkene-1,2,5-triol derivatives

Synthesis of 3-alkenyl-1,2,5-triol derivatives, potentially useful intermediates in organic synthesis, is established, which constitutes stereoselective epoxidation of the hitherto hardly accessible dienyl alcohols of the cis,trans stereochemistry followed by Pd-catalyzed reaction with AcOH.     

Stereoselective synthesis of (E)-β-arylvinyl bromides by microwave-induced reaction of anti-3-aryl-2,3-dibromopropanoic acids using an AgOAc-AcOH system

(E)-β-Arylvinyl bromides were stereoselectively prepared in high yields by microwave irradiation of the corresponding anti-3-aryl-2,3-dibromopropanoic acids in AcOH in the presence of AgOAc for 0.5-3.0 min.     

Synthesis of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and its higher homologs through palladium-catalyzed intramolecular decarboxylative arylation

We report herein an effective method for the construction of 4- and 7-ring benzo-fused thieno[3,2-b]thiophenes, involving palladium-catalyzed intramolecular decarboxylative arylation as the key step.     

Microwave-promoted Suzuki-Miyaura coupling of arylboronic acids with 1-bromo-2-naphthol, o-bromophenol, and o-chlorophenol

In this letter we report a simple and efficient way for the direct Suzuki-Miyaura cross-coupling of unprotected 2-hydroxyaryl bromides and of 2-chlorophenol with arylboronic acids using suitable phosphine/Pd(OAc)₂ catalysts systems with moist K₃PO₄/toluene or moist CsF/dioxane and microwave heating (20 min 105 °C to 3 h 100-120 °C) with an internal temperature control providing 2-hydroxybiaryls in yields up to 98%.     

Efficient microwave-assisted synthesis of 1-(1H-indol-1-yl)-2-phenyl-3-(1H-1,2,4-triazol-1-yl)propan-2-ols as antifungal agents

New conazole antifungals, in the series of triazole alcohols 23a-d and 24a-e incorporating an indole moiety substituted at 5-position by halogens, a cyano or 4-methoxyphenyl group, have been synthesized by ring opening of corresponding oxiranes 15 and 16. These dihalogeno intermediates and their congeneers could be prepared in high yields by Corey-Chaykovsky reaction under microwave irradiation.     

Synthesis of conjugated (1E,3E)- and (1Z,3Z)-1,4-di(n-pyridyl) (or n-quinolyl)-1,3-butadienes from n-(2′-chloroethenyl)pyridine (or quinoline)

The homocoupling reaction between the conjugated n-(2-chloroethenyl)pyridine; n, 2-, 3- and 4- (or quinoline; n, 2- and 4-) mediated by zero-valent nickel complexes at room temperature affords to the corresponding 1,4-diaryl-1,3-butadiene, always as the 1E,3E stereoisomer. The yield in 1,4-diaryl-1,3-butadiene increases with the nickel catalyst and hence, the active zero-valent nickel catalyst is not regenerated during the homocoupling reaction.The stereospecific synthesis of (1Z,3Z)-1,4-di(4′-pyridyl)-1,3-butadiene stereoisomer was efficiently carried out by partial hydrogenation of the appropriate 1,4-di(4′-pyridyl)-1,3-butadiyne.     

Use of cheaper metal than Rh, CHCl3-free Pd catalyst, in 1,2-addition of aromatic aldehydes with arylboronic acids

Pd(OAc)₂-(±)-tol-BINAP-catalyzed arylation reaction of aromatic aldehydes with arylboronic acids in the absence of CHCl₃ is described.     

Totally regio- and stereoselective synthesis of (E)-3-arylidene-3,4-dihydro-2H-1,4-benzoxazines under palladium catalyst

A new, one-pot palladium catalyzed reaction has been developed for the general synthesis of (E)-3-arylidene-3,4-dihydro-2H-1,4-benzoxazines at room temperature. The reaction procedure tolerates various functional groups. The method is characterized by regio- and stereoselectivity, operational simplicity, mild reaction conditions, and short reaction time.     

Stereospecific preparation of symmetrical (1Z, 3Z)- and (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes from 1-bromo-1-fluoroalkenes

A straightforward method to prepare symmetrical (1Z, 3Z)- and (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes is described. High E/Z ratio 1-bromo-1-fluoroalkenes, prepared by isomerization from the E/Z ≈ 1:1 isomeric mixtures, reacted with Bu₃SnSnBu₃ and Pd(PPh₃)₄ to afford (1Z, 3Z)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes in good yield. (Z)-1-Bromo-1-fluoroalkenes, which were prepared by kinetic reduction from 1-bromo-1-fluoroalkenes (E/Z ≈ 1:1), can undergo similar reaction with Bu₃SnSnBu₃ and Pd(PPh₃)₄/CuI to prepare (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes.     

Regiospecific synthesis of symmetrical (1E,3E) 2,3-difluoro-1,4-diphenyl-buta-1,3-dienes via palladium-catalyzed cross-coupling of (Z) 2-bromo-2-fluoroethenylbenzenes in presence of bis(pinacolato)diboron

The cross-coupling reaction of (Z) 1-bromo-1-fluoroalkenes catalyzed by PdCl₂(PPh₃)₂-2PPh₃ (3%) and CsF in Tetrahydrofuran (THF) in presence of bis(pinacolato)diboron led to (1E,3E) 2,3-difluoro-1,4-disubstituted-buta-1,3-dienes in high yields.