Thioether-based copper(I) Schiff base complex as a catalyst for a direct and asymmetric A3-coupling reaction

A novel thiosalen ligand based on a thioether has been prepared and readily coordinated with copper(I) salts (CuCl, CuBr, CuI, and CuCN). The new organometallic catalyst was used for the direct and enantioselective alkynylations of imines in an A³-coupling reaction. In this reaction, the corresponding propargylamines were obtained as single products in excellent yields and with good enantioselectivities.     

Synthesis of symmetric 1,4-diamino-2-butynes via a Cu(I)-catalyzed one-pot A3-coupling/decarboxylative coupling of a propiolic acid, an aldehyde, and an amine

A novel microwave-assisted approach for the one-pot Cu(I)-catalyzed A(3)-coupling/decarboxylative coupling (PA(2)-coupling) of a propiolic acid, an aldehyde, and an amine, resulting in the formation of diversely substituted 1,4-diamino-2-butynes,is described. It is noteworthy that this new multicomponent coupling provides an efficient access to introduce alkyl and aryl group at the 1,4-position of the 1,4-diamino-2-butynes.     

Gold-nanoparticle-catalyzed synthesis of propargylamines: the traditional A3-multicomponent reaction performed as a two-step flow process

The alkyne, aldehyde, amine A(3)-coupling reaction, a traditional multicomponent reaction (MCR), has been investigated as a two-step flow process. The implicated aminoalkylation reaction of phenylacetylene with appropriate aldimine intermediates was catalyzed by gold nanoparticles impregnated on alumina. The aldimine formation was catalyzed by Montmorillonite K10 beforehand. The performance of the process has been investigated with respect to different reaction regimes. Usually, the A(3)-multicomponent reaction is performed as a "one-pot" process. Diversity-oriented syntheses using MCRs often have the shortcoming that only low selectivity and low yields are achieved. We have used a flow-chemistry approach to perform the A(3)-MCR in a sequential manner. In this way, the reaction performance was significantly enhanced in terms of shortened reaction time, and the desired propargylamines were obtained in high yields.     

Diversity oriented microwave-assisted synthesis of (-)-steganacin aza-analogues

A novel microwave-assisted, highly efficient protocol for the synthesis of hitherto unknown aza-analogues of (-)-Steganacin, a naturally occurring bisbenzocyclooctadiene lignan lactone with potent antileukemic and tubulin polymerization inhibitory activity, has been developed. Focused microwave irradiation is demonstrated to be highly beneficial in promoting the three crucial steps of the sequence to effect the final ring closure: the Suzuki-Miyaura reaction, Cu-mediated A3-coupling, as well as the intramolecular Huisgen 1,3-dipolar cycloaddition.     

Regioselective Cu(I)-catalyzed tandem A3-coupling/decarboxylative coupling to 3-amino-1,4-enynes

An efficient and novel copper-mediated protocol for the synthesis of 3-amino-1,4-enynes from glyoxylic acid, an amine, and an alkyne was developed. This new reaction involving two sequential C-C bond formations is air and moisture tolerant and proceeds via a tandem A(3)-coupling and a selective decarboxylative coupling.     

Construction of polymeric Cu(I) N-heterocyclic carbene complex utilizing terpyridine-Fe(II) as linkers: formation of an efficient and recyclable catalyst

A metal-coordination-driven self-assembly using the predesigned building block has been developed. Herein, the catalytic active NHC–Cu(I) units were introduced into the terpyridine metal coordination polymers. The self-assembled architecture, as a heterogeneous catalyst, was successfully used to catalyze the A³-coupling reaction of aldehyde, alkyne, and amine and Huisgen 1,3-dipolar cycloaddition reaction of azide and alkyne in high yields.     

CuSO4-glucose for in situ generation of controlled Cu(I)-Cu(II) bicatalysts: multicomponent reaction of heterocyclic azine and aldehyde with alkyne, and cycloisomerization toward synthesis of N-fused imidazoles

The catalytic efficiency of mixed Cu(I)-Cu(II) system in situ generated by partial reduction of CuSO(4) with glucose in ethanol (nonanhydrous) under open air has been explored. With this catalysis, the multicomponent cascade reaction of A(3)-coupling of heterocyclic amidine with aldehyde and alkyne, 5-exo-dig cycloisomerization, and prototropic shift has afforded an efficient and eco-friendly synthesis of therapeutically important versatile N-fused imidazoles. Diverse heterocyclic amidines, several of which are known to be poorly reactive, and aldehydes are compatible in this catalytic process.     

New 1,2-dithioether based 2D copper(I) coordination polymer: from synthesis to catalytic application in A3-coupling reaction

Abstract

A new 2D copper(I) coordination polymeric complex has been synthesized from CuI and 1-(1-{4-chlorophenylthio}propan-2-ylthio)-4-chlorobenzene ([(CuI)₂{ArSCH₂CH(CH₃)SAr}₂]_n, Ar = 4-ClC₆H₄) and characterized by high resolution mass spectrometry (HRMS) and single crystal X-ray diffraction techniques. The complex has been employed as a suitable catalyst for a solvent-free, one-pot, three-component A³-coupling reaction. A variety of aromatic and aliphatic aldehydes, terminal alkynes and aliphatic cyclic secondary amines have been used to prepare a library of propargylamines using the 2D-Cu complex at significantly low concentration (0.2?mol%).     

Poly(3,3′-dimethoxy-2,2′-bithiophene): Synthesis and comparison with poly(3-methoxythiophene)

A new electroactive polymer, namely poly(3,3′-dimethoxy-2,2′-bithiophene) has been prepared by voltammetric polymerization of 3,3′-dimethoxy-2,2′-bithiophene. Due to a different coupling pattern (equivalent to “head-to-head,” and “tail-to-tail” coupled alkoxythiophene rings), poly(3,3′-dimethoxy-2,2′-bithiophene) exhibits different voltammetric properties than the corresponding “head-to-tail” coupled polymer, i.e., poly(3-methoxythiophene). Poly(3,3′-dimethoxy-2,2′-bithiophene) gives very sharp oxidation and reduction peaks indicating an abrupt insulator to conductor transition. This hypothesis was corroborated by the studies of relative resistance as a function of electrode potential. Sharper and better-defined redox peaks may indicate better stereoregularity of poly(3,3′-dimethoxy-2,2′-bithiophene) as compared to poly(3-methoxythiophene) since in this compound the 5,5′-coupling positions are geometrically equivalent and no coupling defects are expected. © 1992 John Wiley & Sons, Inc.     

Chitosan-supported copper as an efficient and recyclable heterogeneous catalyst for A3/decarboxylative A3-coupling reaction

Chitosan-supported copper (chit@copper) based heterogeneous catalysts have been explored for A³-coupling and decarboxylative A³-coupling. The developed protocol employs low catalyst loading, solventless condition and easy work-up for the synthesis of diversely substituted propargylamines. More importantly, the catalyst could be recovered and reused without any significant loss in the activity. This offer huge advantages as recyclability issues are rarely addressed in decarboxylative A³-coupling. Leaching studies were carried out using AAS and ICPMS analysis. It is envisaged that chit@copper catalysts can have potential applications in terms of efficiency and recyclability in the emerging area of decarboxylative CH bond activation/functionalization strategies.     

Mechanism of Azo Coupling Reactions XXXIII. pH-dependence and micromixing effects on the product distribution of couplings with 6-amino-4-hydroxy-2-naphthalenesulfonic acid. Evidence for N-coupling of a naphthylamine derivative

Azo coupling of 6-amino-4-hydroxy-2-naphthalenesulfonic acid (1) with 3-trifluoromethyl- and 4-nitrobenzenediazonium ion in relative highly concentrated aqueous alkaline solutions gave ratios of aminoazo to hydroxyazo compounds which are much higher than expected on the basis of the acid-base pre-equilibria of 1 . These product ratios are disguised by effects of micromixing. In dilute solution (≤10^?2 mol/l) product ratios and kinetics both correspond to the theory of acid-base pre-equilibria. A bisazo dye 10 was formed as a by-product in couplings with 3-trifluoromethylbenzediazonium ion, as expected for reactions with micromixing effects. In the reaction with benzenediazonium ions, the products of azo coupling of diazotized 1 with 1 (compound 8 ) and of the monoazo compound 8 with benzenediazonium ion (compound 9 ) were found. It is likely that diazotized 1 is formed by N-coupling of 1 with benzenediazonium ion, tautomeric rearrangement and protonation of the triazene to diazotized 1 and aniline. This seems to be the first case of N-coupling of a naphthylamine which was assumed to be capable of C-coupling only.     

Silver chloride supported on Vitamin B1 -Organometallic magnetic catalyst: synthesis,density functional theory study and application in A3-coupling reactions

A highly efficient Fe₃O₄@VitB₁–Ag(I) magnetic catalyst has been obtained using surface modification of Fe₃O₄. To this end, silver chloride was immobilized on Fe₃O₄ nanoparticles via vitamin B₁ biomolecules. The synthesized biocompatible magnetic catalyst was applied in an A³-coupling reaction in the presence of aldehyde, amine and phenyl acetylene under solvent-free conditions and afforded the desired products in excellent yields. Also, interactions between metal and ligand in the Fe₃O₄@VitB₁–Ag(I) were studied using theoretical calculations.     

C3−C3′ and C6−C6′ Oxidative Couplings of Carbazoles

9-Substituted carbazoles are widely used units in materials science, and their oxidative reactions have been utilized for the synthesis and characterization of polymers. Though the oxidative mechanism of carbazoles has been known for a few decades, structural definition has remained difficult, because their polymers are generally insoluble with incomplete characterization and unknown dependence of the electrochemical potentials. The oxidative reactions of 9-substituted carbazoles should be carefully considered under specific oxidative conditions; otherwise, structure definitions could be wrong, because the IR and NMR spectra used previously cannot quantitatively analyze 3,3′-coupling and 6,6′-coupling of carbazoles. In this review, the best understanding of the C3−C3′ and C6−C6′ oxidative couplings of 9-substituted carbazoles is presented, and the benefit of these oxidative reactions from the viewpoints of electrochemical synthesis, film engineering, and the synthesis and processing of polymers is highlighted.     

Synthesis and identification of 2,5-bis-(4-hydroxy-3-methoxyphenyl)-tetrahydrofuran-3,4-dicarboxylic acid, an unanticipated ferulate 8-8-coupling product acylating cereal plant cell walls

A new product implicated in cereal grain polysaccharide cross-linking has been authenticated by independent synthesis. Saponification of cereal grain fiber releases the RRRS/SSSR-isomer of 2,5-bis-(4-hydroxy-3-methoxyphenyl)-tetrahydrofuran-3,4-dicarboxylic acid. The parent ester logically derives from 8-8-coupling of ferulate followed by water addition to one of the incipient quinone methide moieties and internal trapping of the other. The finding adds complexity to the analysis of plant cell wall cross-linking, but provides clues to important polysaccharide cross-linking pathways occurring in planta.     

Single and double A3-coupling (aldehyde-amine-alkyne) reaction catalyzed by an air stable copper(I)-phosphole complex

An air stable copper(I)-phosphole complex, [CuCl{2,5-bis(2-thienyl)-1-phenylphosphole}₂] (1), was utilized as a catalyst in single and double A³-coupling reactions for preparing mono- and bi-propargylamines. A variety of aldehydes, amines and terminal alkynes were tested. Most of these reactions led to formation of the expected propargylamines in good yields using low amounts catalyst and obviating both the use of purified reagents as employ of a glovebox.     

Dihydroquinazolinones via A3-Type Reactions of N-Carbamoyliminium Ions

A variant of the A³ coupling reaction was developed utilizing in situ generated N-carbamoyliminium ions. The tandem INCIC/A³-coupling sequence provided a facile one-pot synthesis of dihydroquinazolinone derivatives. The scope of the reaction was demonstrated in solution as well as on solid support. The reaction was further combined with peptide synthesis, S_NAr reactions, CuAAC triazole formation or bromination, providing additional opportunities for further diversification of the dihydroquinazolinone scaffolds.     

Nafion?NR50 catalyzed A3-coupling for the synthesis of propargylamines via C-H activation

A one-pot, three-component coupling reaction of aldehydes, amines and alkyne (A³-coupling) via C-H activation using perflorinated resinsulphonic acid (Nafion?NR50) as a recyclable and environmentally benign catalyst for the synthesis of propargylamine derivatives is described. This protocol avoids the use of heavy metals, co-catalysts and produces the propargylamines in excellent yields.     

Ag2CO3-catalyzed efficient synthesis of internal or terminal propargylicamines and chalcones via A3-coupling under solvent-free condition

Several simple, fast and practical protocols have been developed to synthesize internal or terminal propargylamines and chalcones via A³-coupling reaction of aldehydes, amines, and alkynes catalyzed by an easily available catalyst Ag₂CO₃ under solvent-free condition. The reaction proceeded smoothly to deliver various products in good-to-excellent yields with good functional group tolerance. Gram-scale preparation, bioactive molecule synthesis and asymmetric substrates have been demonstrated. Furthermore, plausible mechanisms for the synthesis of different products have been proposed.     

19F n.m.r. spectrum of hexafluoroquinazoline long-range inter-ring F?F coupling constants

The ¹⁹F n.m.r. spectrum of hexafluoroquinazoline has been analyzed giving the signs and magnitudes of all but two of the coupling constants, and supporting the analyses of the ¹⁹F n.m.r. spectra of heptafluoroquinoline and heptafluoroisoquinoline. Long range F? F inter-ring coupling constants are a guide for assessing π-electron delocalization pathways. In addition, nitrogen in the β position enhances the distant F-5, F-7 meta-coupling constant, implying a π-contribution to J(FF)meta. A rationalization of changes in peri-coupling constants is also presented. The observed changes appear to be the sum of two effects: (i) ring contraction by the insertion of shorter C? N bonds into the aromatic ring and (ii) a secondary effect which is dependent on the existence of a β-nitrogen, adjacent to the peri nuclei.