Palladium-catalyzed sequential alkylation-alkenylation reactions: application towards the synthesis of polyfunctionalized fused aromatic rings

The synthesis of polyfunctionalized fused aromatic carbo- and heterocycles from aryl iodides and bromoenoates via a tandem palladium-catalyzed aromatic substitution intramolecular Heck sequence is reported. Using Pd(OAc)₂ and tri-2-furylphosphine (TFP) in the presence of norbornene and Cs₂CO₃ in CH₃CN at 85 °C gave a variety of functionalized bi- and tricyclic fused aromatic rings in good yield.     

Palladium-catalyzed sequential alkylation-alkenylation reactions: new three-component coupling leading to oxacycles

A new three-component domino reaction catalyzed by palladium was devised, producing polysubstituted bicyclic molecules in good yields from readily available substrates. The reaction conditions and the scope of the process were examined, and a possible mechanism is proposed. [reaction: see text]     

Use of palladium-mediated allylic substitution reactions in the synthesis of 2,5-disubstituted-2,5-dihydrofurans

2,5-Disubstituted-2,5-dihydrofurans were synthesised in both one- and two-pot reactions starting from 2,5-diacetoxy-2,5-dihydrofuran. These palladium-mediated allylic substitution reactions were useful in preparing symmetrical or unsymmetrical products by employing the same nucleophile twice or two different nucleophiles, respectively.     

A facile synthesis of 3-substituted-2-aminothiophenes and 1,3-disubstituted-2-methylthiopyrroles

Electron-rich 3-functionalized-2-aminothiophenes 6 and 1,3-disubstituted-2-methylthiopyrroles 10 were synthesized from substituted allyl benzotriazoles 2 and isothiocyanates 3 via condensation and subsequent heterocyclization.     

Ring contraction synthesis of 2,5-disubstituted-3-arylamino-4-cyanopyrroles from 2,6-disubstituted-4-arylamino-5-cyanopyrimidines

A method for synthesis of 2,5-disubstituted-3-arylamino-4-cyanopyrroles from newly synthesised 2,6-disubstituted-4-arylamino-5-cyanopyrimidines by treatment with zinc and acetic acid, the yields being up to 80%, is developed.     

Approaches toward the synthesis of 2,5-disubstituted-1,3-thiazolidines

Synthetic approaches for new 2,5-disubstituted-1,3-thiazolidines are described. Steric and electronic effects of the N-substituent of the thiazolidine ring represent the major parameter in the rearrangement process. The nmr studies demonstrate that N-unsubstituted 2,5-disubstituted-1,3-thiazolidines exist as epimeric mixture, while the corresponding N-acetylated analogues exist as a conformer mixture.     

A conveneint synthesis of 1-substituted-2,5(4H)-piperazinediones

1-Substituted-2,5(4H)-piperazinediones are prepared by the Michael addition of acrylonitrile and methyl-acrylate and glycylglycine, DL-alanyl-DL-alanine and DL-alanyl-DL-phenylalanine followed by cyclohydration in refluxing xylenes.     

One-pot synthesis of 2,5-disubstituted-1,3,4-thiadiazoles under ultrasonic irradiation

A facile one-pot synthesis of 2,5-disubstituted-1,3,4-thiadiazoles was achieved by ultrasonic irradiation of a mixture of 1- naphthylacetyl chloride,NH_4CNS,CH_2Cl_2 and PEG-400 for 1.5 h at 10-20℃and subsequent irradiation for 1.5h in the presence of N-arylglycine hydrazides.This method requires short time and gives thiadiazoles in high yields.     

Gas-phase elimination reactions of 4-substituted-2-alkoxythiazoline-5-ones

Gas-phase eliminations of 4-substituted-2-alkoxythiazoline-5-ones have been studied. These compounds eliminate via a six-membered transition state to produce 4-substituted-thiazolidine-2,5-diones. These eliminations are unimolecular first-order reactions. Utilization of this thermolysis reaction in the synthesis of new 4-substituted-thiazolidine-2,5-diones is considered. Additional mechanistic information was obtained by comparing the kinetic data for thermal elimination reactions of these compounds with that of 1-ethoxythiazole. © 1996 John Wiley & Sons, Inc.     

A facile synthesis of methyl 2-substituted-4-benzoxazolecarboxylates

Methyl 2-substituted-4-benzoxazolecarboxylates were synthesized from methyl 2-amino-3-hydroxybenzoate and the corresponding acid chloride or ortho acetal with pyridinium p-toluenesulfonate as an acid catalyst. Decomposition due to hydration at the 2-position was seen for some compounds during purification.     

Palladium-catalyzed reactions for the synthesis of chlorins and 5,10-porphodimethenes

The palladium-catalyzed reaction of RLi with various 5,10,15,20-tetrasubstituted porphyrins offers a convenient synthetic route to chlorins and porphodimethenes (calixphyrins). The reactions utilized various Pd catalysts and CuI and yielded either 2,3-substituted chlorins or 5,10-disubstituted porphodimethenes in yields ranging from 20-40%. The reaction of octaethylporphyrin with t-BuLi in the presence of a Pd-catalyst generated the corresponding 5,10-porphodimethene in 72% yield.     

A general approach for the synthesis of 5-substituted-4-amino-pyrrolidin-2-ones and 5-substituted-4-amino-3-pyrrolin-2-ones

Short stereoselective syntheses of both 5-substituted-4-amino-pyrrolidin-2-ones and 5-substituted-4-amino-3-pyrrolin-2-ones from natural α-amino acids are described.     

Palladium-catalyzed coupling reactions towards the synthesis of well-defined thiophene-oligomers

Heck- and Ullmann-type palladium-catalyzed reactions were used in order to perform the synthesis of 3′,4″-dioctyl-2,2′,5′2″,5″,2′″-tetrathienyl. The desired oligothiophene was synthesized in five steps with a total yield of 38% by a Heck-type reaction of bromo-derivatives and a yield of 45% by an Ullmann-type reaction of iodo-precursors.     

Palladium-catalyzed carbonylative synthesis of N-(2-cyanoaryl)benzamides and sequential synthesis of quinazolinones

A convenient procedure for the synthesis of N-(2-cyanoaryl)benzamides has been developed. Using aryl bromides and 2-aminobenzonitriles as the substrates, Mo(CO)₆ as the CO source, the desired amides were produced in good yields. Quinazolinones were produced in good yields in a sequential manner as well.     

Synthesis,characterization and antimicrobial evaluation of 2,5-disubstituted-4-thiazolidinone derivatives

In the present study novel derivatives of 4-thiazolidinone were prepared from biphenyl-4-carboxylic acid and evaluated for their in vitro antimicrobial activity against two Gram negative strains (Escherichia coli and Pseudomonas aeruginosa) and two Gram positive strains (Bacillus subtilis and Staphylococcus aureus) and fungal strain Candida albicans and Aspergillus niger. The newly synthesized compounds were characterized by IR, ¹H NMR and C, H, N analyses. The results revealed that all synthesized compounds have a significant biological activity against the tested microorganisms. Among the synthesized derivatives 4g (biphenyl-4-carboxylic acid [2-(3-bromophenyl)-5-(3-nitrobenzylidene)-4-oxo-thiazolidin-3-yl]-amide) and 4i (biphenyl-4-carboxylic acid [5-(3-bromobenzylidene)-2-(3-bromophenyl)-4-oxo-thiazolidin-3-yl]-amide) were found to be most effective antimicrobial compounds.     

One-pot synthesis, antibacterial and antifungal activities of novel 2,5-disubstituted-1,3,4-oxadiazoles

A series of novel 2,5-disubstituted-1,3,4-oxadiazoles have been synthesized from long-chain alkanoic and alkenoic acids. The structures of these compounds have been elucidated by elemental and spectral （IR, ^1H NMR, ^13C NMR, MS） analysis. Furthermore, compounds were screened for in vitro antibacterial activity against the representative panel of two Gram-positive and two Gram- negative bacteria. All the synthesized compounds were also tested for their inhibitory action against five strains of fungus. The various compounds show potent inhibitory action against test organisms. 2007 Abdul Rauf. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.     

Facile stereoselective synthesis of 1,3-disubstituted-4-trichloromethyl azetidin-2-ones

The highly stereoselective synthesis of 1,3-disubstituted-4-trichloromethyl azetidin-2-ones by the [2+2] cycloaddition of ketenes with imines derived from chloral is described.     

Palladium-catalyzed Suzuki cross-coupling of 2-haloselenophenes: synthesis of 2-arylselenophenes, 2,5-diarylselenophenes, and 2-arylselenophenyl ketones

We present herein our results on the Suzuki coupling reaction of 2-haloselenophenes with boronic acids catalyzed by palladium salt and describe a new route established to prepare 2-arylselenophenes and 2,5-diarylselenophenes in good yields. The reaction proceeded cleanly under mild conditions and was performed with aryl boronic acids bearing electron-withdrawing, electron-donating, and neutral substituents, in the presence of Pd(OAc)2, K2CO3/H2O in DME. In addition, by this protocol unsymmetrical aryl ketones were also obtained from 2-iodoselenophene and boronic acids via a carbonylative process.