1,721,019 research outputs found
Mild Pd/Cu-Catalyzed Sila-Sonogashira Coupling of (Hetero)aryl Bromides with (Hetero)arylethynylsilanes under PTC Conditions
No full textThe palladium/copper cocatalyzed sila-Sonogashira reaction of (hetero)arylethynysilanes with (hetero)aryl bromides in toluene and water at 40 ̊C under PTC conditions gave the required di(hetero)arylethynes in moderate to high yields. Activated, deactivated and ortho-substituted (hetero)aryl bromides are well tolerated. This protocol also allowed the preparation of symmetrical diarylethynes by double arylation of 1,2-bis(trimethylsilyl)ethyne
Selective Palladium-Catalyzed Suzuki–Miyaura Reactions of Polyhalogenated Heteroarenes
No full textThe palladium-catalyzed Suzuki–Miyaura reaction of multiply halogenated, electron-rich and electron-deficient heteroarenes is one of the most reliable and environmentally friendly tools for installing a wide range of non-functionalized and functionalized carbon substituents onto heteroaromatic systems with exquisite chemo- and site-selectivity. For substrates with different halogen groups the chemoselectivity of the Suzuki–Miyaura reactions has been found to be dependent on the reactivity difference between the halogens. However, the hardest achievement of selectivity in Suzuki–Miyaura monocouplings involving polyhalogenated heteroarenes with identical halogen atoms has been shown to be dominated by steric and electronic effects and the presence of directing groups at positions neighbouring the reaction sites. Moreover, in the case of symmetrically substituted dihaloheteroarenes with identical halogen atoms, highly selective monocoupling reactions have often been achieved only after a careful optimization of reaction parameters including the catalyst precursor, base, solvent, and the molar ratio between electrophile and organoboron reagent. This critical review with 341 references covers developments on the chemo- and site-selective Suzuki–Miyaura monocoupling reactions of polyhalogenated heteroarenes with different or identical halogen atoms. It also includes the synthesis of polysubstituted heteroarenes, not easily accessible by other means, via consecutive monocoupling reactions and/or a more synthetically valuable approach involving one-pot polycoupling reactions
Mild Palladium-Catalyzed Regioselective Direct Arylation of Azoles Promoted by Tetrabutylammonium Acetate
Full text linkA mild, general, and convenient palladium-catalyzed direct arylation of the 5-position of azoles with aryl bromides, efficiently promoted by tetrabutylammonium acetate, is described. 1-Methylpyrazole, oxazole, and thiazole reacted at 70 degrees C in N,N-dimethylacetamide by using Pd(OAc)(2) as the catalyst precursor. Electron-poor and -rich functional groups, including the free hydroxy group, are well tolerated in the electrophilic partner. A variety of 5-aryl-1-methylimidazoles were also very efficiently obtained simply by raising the reaction temperature to 110 degrees C. This ligand-free protocol was successfully applied to the one-pot synthesis of two bioactive natural compounds, balsoxin and texaline, starting from oxazole by sequential direct arylation of the 5- and 2-positions
Direct (Hetero)arylation Reactions of (Hetero)arenes as Tools for the Step- and Atom-Economical Synthesis of Biologically Active Unnatural Compounds Including Pharmaceutical Targets
No full textThe significant number of papers and reviews published in this last decade testifies to the utility of the transition-metal-catalyzed direct C–H (hetero)arylation reactions of (hetero)arenes as efficient and powerful tools for the step- and atom-economical, regio- and chemoselective synthesis of natural and unnatural compounds. However, no review has so far been devoted to summarizing the application of these reactions in the synthesis of biologically active compounds. This review with 341 references aims to fill this gap, providing a comprehensive picture of the transition-metal-catalyzed intra- and intermolecular direct C–H (hetero)arylation reactions of (hetero)arenes with (hetero)aryl halides or pseudohalides that have been used as key steps of syntheses of unnatural biologically relevant compounds including pharmaceutical targets, up to the end of September 2015. Attention has also been directed to provide a brief description of the biological properties of the synthesized compounds. 1 Introduction 2 Syntheses via Intramolecular Direct (Hetero)arylation of (Hetero)arene Derivatives 3 Syntheses via Intermolecular Direct (Hetero)arylation Reactions 3.1 Of Arenes 3.2 Of Five-Membered Heteroarenes with One Heteroatom 3.3 Of Five-Membered Heteroarenes with Two Heteroatoms 3.4 Of Five-Membered Heteroarenes with Three and Four Heteroatoms 3.5 Of Five-Membered Heteroarenes Fused to a Six-Membered Heteroarene 3.6 Of Five-Membered Heteroarene Moieties of Tricyclic Heteroarenes 3.7 Of Six-Membered Heteroarenes 4 Syntheses of Nitrogen-Containing Polycyclic Heteroarene via One-Pot Palladium-Catalyzed Domino Direct Arylation/N-Arylation Reactions 5 Conclusion
Imidazole analogues of resveratrol: synthesis and cancer cell growth evaluation
Full text linkNovel trans-restricted analogues of resveratrol in which the CeC double bond of the natural derivative has been replaced by diaryl substituted imidazole analogues have been designed. The syntheses of 1,4-, 2,4-, and 2,5-diarylimidazoles, in which the two aryl moieties are linked to the heteroaromatic core in a 1,3 fashion in order to preserve the trans stereochemistry, have been successfully carried out by re- gioselective sequential transition metal-catalyzed arylations of simple, commercially available imidazole precursors. The anticancer activity of selected analogues has been evaluated in vitro against the NCI-60 human tumor cell lines panel. From this screening, we were able to select a synthetic candidate that resulted more active than its natural lead
Development and applications of highly selective palladium-catalyzed monocoupling reactions of (cyclo)alkenes and 1,3-alkadienes bearing two or three electrophilic sites and bis(enol triflates) with terminal alkynes
Full text linkThe motivation for writing this review with 558 references, which covers the literature up to the end of September 2012, is to fill a part of this gap by illustrating highly selective Pd/Cu-catalyzed and Cu-free Pd-catalyzed monoalkynylation reactions of (cyclo)alkenes and 1,3-butadienes bearing two or three identical or different electrophilic sites and bis(enol triflates) with terminal alkynes. However, Pd-catalyzed selective monocoupling reactions of 1-alkynes with (hetero)aryl halides or pseudohalides with two identical or different electrophilic sites will not be covered. Moreover, Pd-catalyzed monocoupling reactions of 1-alkynes with non-conjugated diene systems bearing an electrophilic site on each carbon–carbon double bond have also been considered to be beyond the scope of this review.
In addition to describing and commenting on the aforementioned monoalkynylation reactions of (cyclo)alkenes and 1,3-dienes with two or three identical or different electrophilic sites and bis(enol triflates), emphasis has been placed on the use of Pd-catalyzed monoalkynylations of (cyclo)alkenes and 1,3-butadienes bearing two or three identical or different electrophilic sites and bis(enol triflates) as key steps of the syntheses of core structures and models of enediyne antitumor antibiotics, pharmacologically active compounds, and bioactive naturally occurring compounds including insect sex pheromone components, and fungal and plant metabolites. Moreover, the review has been focused on the formation of disubstituted acetylenic derivatives by one-pot site-selective Pd-catalyzed consecutive alkynylation reactions of di(pseudo)halogenated olefinic substrates with two different terminal alkynes. Where appropriate, the reasons for the observed stereo-, site-, and/or chemoselectivities of the reported Sonogashira-type monoalkynylation reactions have been mentioned and discussed
Remarkable Efficiency Improvement in the Preparation of Insoluble Polymer-Bound (IPB) Enantioselective Catalytic Systems by the Use of Silicone Chemistry
No full textThe use of platinum-catalyzed hydrosilylation chemistry of silicones greatly simplifies the preparation of bis-oxazoline (box) ligands covalently bound to an insoluble polymeric support. The use of such immobilized chiral ligands in different copper-catalyzed asymmetric transformations (carbonyl-ene, Mukaiyama aldol and olefin cyclopropanation reactions) allows the attainment of high levels of enantioselectivity (91-99 % ee)
Imidazole-Fused Enediynes by Selective C5–C4 Alkynylations of 4,5-Dibromoimidazoles
Full text linkAn efficient synthesis of symmetrical 1,2-disubstituted 4,5-dialkynylimidazoles by Sonogashira alkynylation of the corresponding 4,5-dibromo derivatives was developed. Moreover, through a careful tuning of the palladium ligand, unsymmetrical 1,2-disusbtituted 4,5-dialkynylimidazoles were also prepared through a regioselective C5 alkynylation of 4,5-dibromoimidazoles, followed by a second alkynylation involving the 4-bromo derivatives so obtained. This interesting class of imidazole-fused enediynes is also able to give thermal Bergman cycloaromatization (BC), as proved by DSC experiments
Synthesis of Multiply Arylated Heteroarenes, including Bioactive Derivatives, via Palladium-Catalyzed Direct C?H Arylation of Heteroarenes with (Pseudo)Aryl Halides or Aryliodonium Salts
No full textThis review with 387 references covers the literature un- til the end of November 2013 on the synthesis of multiply arylated heteroarenes via highly selective palladium-catalyzed direct C–H arylation reactions of heteroarene derivatives with aryl halides or pseudohalides or aryliodonium salts. Particular attention has been made to describe the synthesis of biologically active compounds and substances that are privileged structural motifs in organic mate- rials. The practicality, versatility, and limitations of the various de- veloped arylation protocols are discussed
Achievement of regioselectivity in transition metal-catalyzed direct C–H (hetero)arylation reactions of heteroarenes with one heteroatom through the use of removable protecting/blocking substituents or traceless directing groups
Full text linkThis review with 453 references covers the literature up to the end of April 2015 on the transition metal-catalyzed direct C-H (hetero)arylation reactions of heteroarenes with one heteroatom in which high regioselectivity has been gained by the use of removable protecting/blocking substituents or traceless directing groups. Particular attention has been devoted to illustrate the typical features of these methods, and to summarize the synthetic procedures used for the introduction of removable protecting/blocking groups in the heteroarene substrates and their subsequent removal from the reaction products. The limitations related to the use of protecting/blocking substituents and directing groups, such as an increase in synthetic steps or the fact that, in many cases, the (hetero)arylation reactions assisted by directing groups involve only C-H bonds ortho to the directing group, will also be highlighted
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