Solvent-free synthesis of propargylamines: an overview

Copper(I) complexes bearing pyrrole-bridged S,N and N-donor ligands as catalysts for tandem hydroamination-alkynylation: effect of anions on product formation

In this study, the reaction between 2-(3,5-dimethylpyrazolylmethyl)-5-(dimethylaminomethyl)pyrrole and thiophenol under heating conditions afforded the new ligand 2-(3,5-dimethylpyrazolylmethyl)-5-(phenylthiomethyl)pyrrole 2. The reaction of 2 with meta-chloroperbenzoic acid provided sulfoxide 3 and sulfone 4 group-containing ligands. The reaction of 2 with copper(I) halides provided the binuclear complexes [Cu(μ-X){μ-C4H3N-2-(CH2Me2pz)-5-(CH2SPh)-κ2-S,N}]2 (X = Cl, Br and I, 5-7) in high yields. Conversely, the analogous reaction of 4 with copper(I) halides yielded two types of complexes, three coordinate bi- and mononuclear of the type [Cu(μ-Cl){C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}]28 and [CuX{C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}2], X = Br, 9 and I, 10. When the reaction was carried out in the presence of KPF6, the two-coordinate complex [Cu{C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}2]PF6-11a was isolated, whereas its BF4- analogue 11b was synthesized by the reaction of 8 with AgBF4. The structures of these complexes were determined using single-crystal X-ray crystallography. These copper complexes catalyzed the hydroamination-alkynylation reaction between several secondary amines and alkyl and aryl terminal alkynes. Using 1 mol% of complexes 5-10 as catalysts, both tri- and tetra-substituted propargylamines were isolated. Alternatively, phenylacetylene and different secondary amines afforded the corresponding trisubstituted propargylamines as the major products and alkyl terminal alkynes gave the tetrasubstituted products in excellent yields. In addition, the role of counter anions such as TfO-, PF6-, BF4-, PO43- and Ph4B- on the product selectivity was studied. When fluorinated anions such as TfO-, PF6-, and BF4- were present with the copper complexes, the hydroamination-hydrovinylation product 1-aminodiene 23 was observed, which was not formed with PO43-, Ph4B- or halide ions. Specifically, TfO- and PF6- favored the formation of 23, while BF4- favored the tetrasubstituted product as the major product. This was further supported by the isolated copper(I) complexes containing PF6- and BF4- and by other specific reactions. The peaks for enamines and [LCu]+ species in the HRMS spectra of the reaction mixtures and the isolation of the morpholinium copper(I) salt support the proposed mechanism.

Silver and Gold Complexes with NHC-Ligands Derived from Caffeine: Catalytic and Pharmacological Activity

N-heterocyclic carbene (NHC) silver(I) and gold(I) complexes have found different applications in various research fields, as in medicinal chemistry for their antiproliferative, anticancer, and antibacterial activity, and in chemistry as innovative and effective catalysts. The possibility of modulating the physicochemical properties, by acting on their ligands and substituents, makes them versatile tools for the development of novel metal-based compounds, mostly as anticancer compounds. As it is known, chemotherapy is commonly adopted for the clinical treatment of different cancers, even though its efficacy is hampered by several factors. Thus, the development of more effective and less toxic drugs is still an urgent need. Herein, we reported the synthesis and characterization of new silver(I) and gold(I) complexes stabilized by caffeine-derived NHC ligands, together with their biological and catalytic activities. Our data highlight the interesting properties of this series as effective catalysts in A3-coupling and hydroamination reactions and as promising anticancer, anti-inflammatory, and antioxidant agents. The ability of these complexes in regulating different pathological aspects, and often co-promoting causes, of cancer makes them ideal leads to be further structurally functionalized and investigated.

Bisphospholane Josiphos-type Ligands in Rhodium Asymmetric Catalysis

Asymmetric catalysis has become a universal and powerful method for constructing chiral compounds. In rhodium asymmetric catalysis, bisphospholane Josiphos-type ligands and their rhodium complexes are receiving increasing attention. This review provides comprehensive information on the bisphospholane Josiphos-type ligands in rhodium asymmetric catalysis. The scope of the literature covers from 2013 to now. The application of bisphospholane Josiphos-type ligands in rhodium asymmetric catalysis is summarized as follows: (i) asymmetric addition to C(sp2 )-C(sp2 ) bonds, (ii) asymmetric addition to C(sp2 )-C(sp) bonds of allenes, (iii) asymmetric hydrogenation of C(sp2 )-N bonds, C(sp2 )-O bonds and pyridinium salts, and (iv) asymmetric silanization of C-H and O-H bonds.

N-Heterocyclic Carbene Silver Complex Modified Polyacrylonitrile Fiber/MIL-101(Cr) Composite as Efficient Chiral Catalyst for Three-Component Coupling Reaction

Complex asymmetric synthesis can be realized by the chiral induction of amino acids in nature. It is of great significance to design a new biomimetic catalytic system for asymmetric synthesis. In this context, we report the preparation and characterization of the composite of polyacrylonitrile fiber (PANF) and metal-organic framework to catalyze the chiral synthesis of propargylamines. A confined microenvironment is established with N-heterocyclic carbene (NHC) silver complex-supported PANF and D-proline-encapsulated MIL-101(Cr). This novel supported catalyst demonstrated high activity in addition to excellent stereoselectivity in the three-component reaction between alkynes, aldehydes, and amines (A3). The regeneration can be realized by adsorption of D-proline again when the stereoselectivity decreases after recycle uses. By regulating the confined microenvironment on the composite, the activity and selectivity of the catalytic system are improved with turnover numbers of up to 2800 and 98% ee. The biomimetic catalytic system to A3 coupling reaction is systematically studied, and the synergistic catalytic mechanism between NHC-Ag and D-proline in the confined microenvironment is revealed.

Gold nanoparticle decorated dithiocarbamate modified natural boehmite as a catalyst for the synthesis of biologically essential propargylamines

Here, we prepare an Au NP decorated dithiocarbamate functionalized boehmite (γ-AlO(OH)@C-NHCS2H·AuNPs). This stepwise synthetic method gives an efficient, cost-effective, and green heterogenous Au-based nanocatalyst for the A3-coupling preparation of the biologically essential propargylamines. Different characterization methods, including FT-IR, XRD, SEM, TEM, EDX spectra, and elemental SEM-mapping, were employed to investigate the structure of the manufactured γ-AlO(OH)@C-NHCS2H·AuNPs. Then we used the prepared composite as a heterogeneous gold-based nanocatalyst for the one-pot A3-coupling preparation of propargyl amines by reacting a variety of aldehydes, amines, and phenylacetylene which exhibited promising results.

A metal-free BF3·OEt2 mediated chemoselective protocol for the synthesis of propargylic cyclic imines

A chemoselective and metal/additive-free protocol for the synthesis of propargylic cyclic imine derivatives via (3 + 2)-cycloaddition of donor-acceptor cyclopropanes and alkynylnitriles in the presence of BF₃·OEt₂ has been established. The newly developed methodology provided access to a variety of propargylic cyclic imines in good to excellent yields. In addition, the synthesis of propargylic amines and the corresponding very stable enol derivatives from the title compound is also explored.

Metal–organic framework (MOF)-, covalent-organic framework (COF)-, and porous-organic polymers (POP)-catalyzed selective C–H bond activation and functionalization reactions

The review summarizes the state-of-the-art of C–H active transformations over crystalline and amorphous porous materials as new emerging heterogeneous (photo)catalysts.

One-Pot Synthesis of Symmetrical and Asymmetrical 3-Amino Diynes via Cu(I)-Catalyzed Reaction of Enaminones with Terminal Alkynes

An economical and efficient protocol for the direct construction of amino skipped diynes through the Cu(I)-catalyzed reaction of enaminones and terminal alkynes has been described. Different kinds of symmetrical and asymmetrical 3-amino diynes could be obtained in up to 83% yield through a one-pot reaction under mild conditions.