87,290 research outputs found
Regioselective Direct C-5 arylation of Imidazoles: synthetic protocols and applications
No full textArylazoles are ubiquitous features of natural products, pharmaceutics, agrochemicals and fluorescent dyes and this, undoubtedly, plays a key role in the continuing search for the development of new, efficient and cost-effective methods to synthesize these heterocycles. Recently, the transition metal-promoted direct C–H arylation of heteroarenes with (hetero)aryl halides has emerged as an attractive strategy for the effective formation of heteroaryl–(hetero)aryl bonds. In fact, this strategy, unlike the traditional metal-catalyzed cross-coupling procedures involving the use of preformed organometallic reagents, enables the direct elaboration of the heterocyclic cores without the need of preactivating both the coupling partners.
In this context, we have been interested in studies aimed to develop efficient protocols for the highly regioselective synthesis of (hetero)aryl azoles by palladium-catalyzed intermolecular direct (hetero)arylation of azoles with (hetero)aryl halides.1 Our studies in this field allowed us the design and development of convenient procedures for the highly regioselective Pd(OAc)2/(2-furyl)3P-catalyzed direct C-5 arylation of 1-aryl-1H-imidazoles, 1-methyl-, 1-benzyl- and 1-methoxymethyl-1H-imidazole with (hetero)aryl iodides and bromides.
These arylation reactions were successfully used as key steps of efficient and highly regioselective syntheses of 1,5-, 2,4(5)-, 4,5-diaryl-1H-imidazole derivatives and 2,4,5-triaryl-1H-imidazoles.
Interestingly, these new synthetic protocols also allowed us to prepare some interesting bioactive arylazole derivatives, which include several cis-restricted analogues of Combretastatin A-4, a potent and selective antitumor derivative.
1) For a review, see: Bellina, F.; Cauteruccio, S.; Rossi, R. Curr. Org. Chem. accepted for publication
Transition Metal-Catalyzed Direct Arylation of Substrates with Activated sp3-Hybridized C–H Bonds and Some Their Synthetic Equivalents with Aryl Halides and Pseudohalides
No full textA study was conducted to demonstrate transition metal-catalyzed direct arylation of substrates with activated sp3-hybridized C-H bonds and some of their synthetic equivalents with aryl halides and pseudohalides. The study also focused on the catalyst system and experimental conditions used for the regioselective synthesis of α-arylated compounds through transition metal-catalyzed arylation of synthetic equivalents of carbonyl compounds. The synthetic equivalents of carbonyl compounds included silyl enol ethers and enol ethers of ketones and silyl ketone acetals using aryl halides or pseudohalides as electrophiles. The investigations also highlighted the utility of these experimentally simple reactions that proceeded without requiring preparation of stoichiometric amounts of organometallics
Regiocontrolled Synthesis of 1,2- Diaryl 1H imidazoles by Palladium and Copper Mediated Diorect Coupling of 1-Aryl-1H-Imidazoles with Aryl Halides under ligandless conditions
No full textA large variety of 1,2-diaryl-1H-imidazoles, including a selective
COX-2 inhibitor, have been regioselectively synthesised
in moderate to high yields by direct coupling of 1-aryl-
1H-imidazoles with aryl iodides or bromides in DMF in the
presence of CsF and catalytic amounts of Pd(OAc)2 under
ligandless conditions. A possible mechanism for this new
highly regioselective C-2 arylation reaction, involving the
formation of an organocopper(I) derivatives followed by a
transmetallation reaction with an arylpalladium(II) halide
Introduction
Imidazoles possessing two aryl substituents appear frequently
in molecules that elicit important biological responses.
Thus, some 1,5-diaryl-1H-imidazoles 1 (Figure 1)
include substances that act as selective inhibitors of cyclooxygenase-
2 (COX-2)[1] and are cytotoxic against a variety
of human cancer cell lines.[2] On the other hand, some 1,2-
diaryl-1H-imidazoles 2 have been reported to be antagonists
of the cannabinoid CB1 receptor[3,4] or to be able to
inhibit COX-2 selectively.[5,6,7] The biological activities of
compounds 1 and 2 have made them popular synthetic targets,
and numerous methods for the synthesis of these heterocycles
have been developed.[8,9] These synthetic methods,
however, involve the construction of the imidazole ring by
multi-step reaction sequences and, before our studies, no
simple and straightforward synthesis of compounds 1 and
2 had been described, with the exception of that of com-
[a] Dipartimento di Chimica e Chimica Industriale, University of
Pisa,
Via Risorgimento 35, 56126 Pisa, Italy
Fax: +39-0502219260
E-mail: [email protected], [email protected]
[b] Dipartimento S.T.A.A.M., Universiy of Molise,
86100 Campobasso, Italy
[c] Istituto di Metodologie Chimiche, CNR,
via Salaria Km 29.300, 00016 Monterotondo Stazione, Roma,
Italy
[d] University of Provence, Jeune Equipe Traces, Centre de Saint-
Jerome,
Case 511, 13397 Marseille Cedex, France
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Eur. J. Org. Chem. 2006, 693–703 © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 693
species and a reductive elimination, is proposed. New onestep
procedures for the synthesis of 1,2,5-triaryl-1H-imidazoles,
based on palladium- and copper-mediated arylation
of 1-aryl-1H-imidazoles, have also been developed. Interestingly,
some imidazole derivatives prepared in this study have
been found to exhibit significant cytotoxic activity against
some human tumour cell lines
Diagonal material matrices for arbitrary simplicial meshes for solving poisson problems with one unknown per element
No full textWe present a technique to construct diagonal material matrices for arbitrary triangular and tetrahedral meshes and arbitrary scalar material parameters. The recipe is based on a novel dual complex called folded Voronoï diagram. The proposed matrices are tailored to enable the use of a complementary-dual formulation for Poisson problems featuring one unknown per element
Computation of the magnetostatic field by means of a mixed analytical-numerical procedure
No full textThe paper deals with a procedure for the computation of the magnetostatic field in a vacuum. A very short summary of some usual methods for the field computation is given first, recalling their advantages and drawbacks, then a mixed analytical–numerical method is presented, which makes use of the analytical solution of Biot–Savart’s integral for simple elementary space domains. The method permits to obtain an accurate solution for a wide set of field source geometries, even when the field is computed inside the sources. In the end, examples of application of the method are presented
Identification of the plasma contour in a RFP configuration
No full textThe paper describes a method for the identification of the plasma shape in a toroidal device for fusion experiments based on magnetic confinement. The method, developed for the RFX machine, makes use of the magnetic measurements and takes into account the electromagnetic effects of a conductive vacuum vessel and of a stabilizing shell. These effects are quite important in "fast" machines such as the RFPs of the present generation
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