p‐TSA Catalyzed Synthesis of 2,4,5‐Triarylimidazoles from Ammonium Heptamolybdate Tetrahydrate in TBAI

A one‐pot synthesis of 2,4,5‐trisubstituted imidazoles from 1,2‐diketone or α‐hydroxy ketone, aldehyde and ammonium heptamolybdate tetrahydrate in an inexpensive and readily available ionic liquid, tetrabutylammonium iodide (TBAI) in molten state using catalytic amounts of p‐TSA has been described.     

Novel Disubstituted Phenylene‐Linked Bis‐imidazole Derivatives: Facile Synthesis and Optical Properties

Six novel disubstituted phenylene‐linked bis‐imidazole derivatives, 3a – 3f , were prepared by a one‐pot, microwave‐assisted method under solvent‐free conditions, in yields ranging from 61.6 to 85.6%. The new compounds were characterized by ¹H‐ and ¹³C‐NMR, UV/VIS, and fluorescence spectroscopy, and mass spectrometry, as well as by elemental analyses. The influence of substituents and solvents on the optical properties of 3a – 3f was investigated. It was found that there is little influence on absorption and excitation spectra in contrast to emission spectra. Compounds 3a – 3f exhibit strong fluorescence in solution, their fluorescence quantum yields ranging from 0.27 to 0.96.     

Palladium-catalyzed hydroarylation of alkynes with arylboronic acids

Reaction of symmetrical and unsymmetrical alkynes with arylboronic acids, using PdCl₂ as catalyst source and i-Pr₂NPPh₂ as ligand, afforded trisubstituted alkenes with regioselectivity in good to excellent yields without a common additional acetic acid. Its efficiency has been demonstrated by its good functional groups, high yield and crowded substrates.     

Chemo-, regio- and stereoselective addition of triorganoindium reagents to acetates of Baylis-Hillman adducts: a new strategy for the synthesis of (E)- and (Z)-trisubstituted alkenes

The addition of several trialkyl or triarylindium reagents to the acetates of Baylis-Hillman adducts proceeds readily under the catalysis of copper and palladium derivatives. The reactions of trialkylindiums are catalyzed efficiently by CuI whereas additions of triarylindiums produce better results with Pd(PPh₃)₄. The reactions with 3-acetoxy-2-methylenealkanoates provide (E)-alkenes, whereas similar reactions with 3-acetoxy-2-methylenealkanenitriles lead to (Z)-alkenes. All the reactions are highly regio- and stereoselective and high yielding.     

A Straightforward Method for the Synthesis of Functionalized Trisubstituted Alkenes through Na2S/Al2O3 Catalyzed Knoevenagel Condensation

Na₂S/Al₂O₃ catalyzed the Knoevenagel condensation between an aldehyde and an active methylene compound to yield various trisubstituted alkenes.     

Phenanthroimidazoles,IV

Syntheses of 1H-phenanthro(9,10-d)imidazoles with naphthyl and thienyl substituents at position 2 are described.

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Phenanthroimidazole, IV. (Kurze Mitteilung)

Zusammenfassung Die Darstellung von drei 1H-Phenanthro(9,10-d)imidazolen mit Naphthylund Thienyl-Substituenten in 2-Stellung wird beschrieben.

     

Synthesis and reactions of 1-(4-chloro-, 3-chloro-, 2-chloro-, 2,4-dichloro-, and 2,4-difluorophenyl)-6,6-dimethyl-4-oxo-4,5,6,7-tetrahydroindazoles

Reaction of the potassium salt of 2-formyldimedone with hydrochlorides of 4-chloro-, 3-chloro-, 2-chloro-, 2,4-dichloro-, and 2,4-difluorophenylhydrazines gave the corresponding 2-arylhydrazinomethylene-dimedones which cyclized in acid media to 1-substituted 6,6-dimethyl-4-oxo-4,5,6,7-tetrahydroindazoles. Oxidation of the latter with selenious acid gave the corresponding 4,5-dioxo-4,5,6,7-tetrahydroindazoles which were further converted into 3-aryl-5,5-dimethyl-4,5-dihydro-3H-pyrazolo[4,3-a]phenazines and 2,6-diaryl-4,4-dimethyl-4,5-dihydro-1H(3H)-indazolo[4,5-g]imidazoles.Riga Technical University, Riga LV-1658, Latvia; e-mail: marina@osi.lv. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, 533–539, April, 2000.     

Palladium-catalyzed coupling of N-tosylhydrazones with ortho substituted aryl halides: synthesis of 4-arylchromenes and related heterocycles

A convenient and efficient procedure for the synthesis of 4-arylchromenes, thiochromenes, and related heterocycles via a four step-sequence has been developed. The first three steps, which involve hydration of alkynes, hydrazones formation, and their Pd-coupling with ortho substituted aryl halides, furnished stereoselectively Z-trisubstituted olefins without any purification of the intermediates generated in each stage. These latter proved to be suitable precursors, in the last step, for the synthesis of the desired heterocycles of biological interest.