Copper-catalyzed decarboxylative coupling reactions for the synthesis of propargyl amines

Recent Advances in the Synthesis of Propargyl Derivatives, and Their Application as Synthetic Intermediates and Building Blocks

The propargyl group is a highly versatile moiety whose introduction into small-molecule building blocks opens up new synthetic pathways for further elaboration. The last decade has witnessed remarkable progress in both the synthesis of propargylation agents and their application in the synthesis and functionalization of more elaborate/complex building blocks and intermediates. The goal of this review is to highlight these exciting advances and to underscore their impact.

Metal-Catalysed A3 Coupling Methodologies: Classification and Visualisation

The multicomponent reaction of aldehydes, amines, and alkynes, known as A3 coupling, yields propargylamines, a valuable organic scaffold, and has received significant interest and attention in the last years. In order to fully realise the potential of the metal-based catalytic protocols that facilitate this transformation, we summarise substrates, in situ and well-characterised synthetic methods that provide this scaffold and attempt a monumental classification considering several variables (Metal, Coordinating atom(s), Ligand type and name, in-situ or well-characterised, co-catalyst, catalyst and ligand Loading (mol%), solvent, volume, atmosphere, temperature, microwave, time, yield, selectivity (e.e. d.r.), substrate name, functionality, loading (amines, aldehydes, alkynes), and use of molecular sieves). This pioneering work creates a valuable database that contains 2376 entries and allows us to produce graphs and better visualise their impact on the reaction.

Metal- and Solvent-Free Multicomponent Decarboxylative A3-Coupling for the Synthesis of Propargylamines: Experimental, Computational, and Biological Investigations

Decarboxylative A³-coupling of ortho-hydroxybenzaldehydes, secondary amines, and alkynoic acids is performed under catalyst and solvent-free conditions. The developed methodology provided a waste-free method for the synthesis of hydroxylated propargylamines which are versatile precursors for various bioactive heterocyclic scaffolds. The experimental and density functional theory studies revealed that the in situ-formed ortho-quinonoid intermediate (formed from ortho-hydroxybenzaldehyde and amine) undergoes a concerted Eschweiler-Clarke type decarboxylation with alkynoic acids. The synthesized compounds were evaluated for MAO-A, MAO-B, and AChE inhibitory activities as potential drug candidates for the treatment of various neurological disorders. Compound 4f was found to be the most potent and selective MAO-B (high selectivity over MAO-A) and AChE inhibitor in the series with IC₅₀ values of 4.27 ± 0.07 and 0.79 ± 0.03 μM, respectively.

Palladium-catalyzed decarboxylative gem-selective addition of alkynoic acids to terminal alkynes

Alkynoic acids added to terminal alkynes to give gem-1,3-enynes with high selectivity and good yields. In addition, the reaction of alkynoic acids with propiolic acid provided the corresponding gem-1,3-enynes via double decarboxylation.

ZnCl2 loaded TiO2 nanomaterial: an efficient green catalyst to one-pot solvent-free synthesis of propargylamines

One-pot green synthesis of propargylamines using ZnCl₂ loaded TiO₂ nanomaterial under solvent-free conditions has been effectively accomplished. The aromatic aldehydes, amines, and phenylacetylene were reacted at 100 °C in the presence of the resultant catalyst to form propargylamines. The nanocrystalline TiO₂ was initially synthesized by a sol-gel method from titanium(iv) isopropoxide (TTIP) and further subjected to ZnCl₂ loading by a wet impregnation method. X-ray diffraction (XRD) patterns revealed the formation of crystalline anatase phase TiO₂. Field emission scanning electron microscopy (FESEM) showed the formation of agglomerated spheroid shaped particles having a size in the range of 25-45 nm. Transmission electron microscopy (TEM) validates cubical faceted and nanospheroid-like morphological features with clear faceted edges for the pure TiO₂ sample. Surface loading of ZnCl₂ on spheroid TiO₂ nanoparticles is evident in the case of the ZnCl₂ loaded TiO₂ sample. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ti⁴⁺ and Zn²⁺ species in the ZnCl₂ loaded TiO₂ catalyst. Energy-dispersive X-ray (EDS) spectroscopy also confirmed the existence of Ti, O, Zn and Cl elements in the nanostructured catalyst. 15% ZnCl₂ loaded TiO₂ afforded the highest 97% yield for 3-(1-morpholino-3-phenylprop-2-ynyl)phenol, 2-(1-morpholino-3-phenylprop-2-ynyl)phenol and 4-(1,3-diphenylprop-2-ynyl)morpholine under solvent-free and aerobic conditions. The proposed nanostructure-based heterogeneous catalytic reaction protocol is sustainable, environment-friendly and offers economic viability in terms of recyclability of the catalyst.

Synthetic Access to Secondary Propargylamines via a Copper-Catalyzed Oxidative Deamination/Alkynylation Cascade

A novel and selective cascade reaction of primary amines and alkynes for the synthesis of the corresponding secondary propargylamines is described. This protocol proceeds with a CuBr₂/TBHP system through a process of oxidative deamination of primary amines to imine and alkynylation, featuring a wide scope of substrates with good functional-group tolerance and operational simplicity. Additionally, the use of two different primary amines could also work smoothly using this protocol.

Synthesis and Reactivity of Propargylamines in Organic Chemistry

Propargylamines are a versatile class of compounds which find broad application in many fields of chemistry. This review aims to describe the different strategies developed so far for the synthesis of propargylamines and their derivatives as well as to highlight their reactivity and use as building blocks in the synthesis of chemically relevant organic compounds. In the first part of the review, the different synthetic approaches to synthesize propargylamines, such as A³ couplings and C-H functionalization of alkynes, have been described and organized on the basis of the catalysts employed in the syntheses. Both racemic and enantioselective approaches have been reported. In the second part, an overview of the transformations of propargylamines into heterocyclic compounds such as pyrroles, pyridines, thiazoles, and oxazoles, as well as other relevant organic derivatives, is presented.

Zn(ii) anchored onto the magnetic natural hydroxyapatite (ZnII/HAP/Fe3O4): as a novel, green and recyclable catalyst for A3-coupling reaction towards propargylamine synthesis under solvent-free conditions

In this paper, Zn(ii) anchored onto the magnetic natural hydroxyapatite (Zn^II/HAP/Fe₃O₄), as a new and magnetically recoverable catalyst, was prepared and characterized using different techniques such as FT-IR, XRD, TGA, TEM, EDX, VSM and ICP.

Additive-free decarboxylative coupling of cinnamic acid derivatives in water: synthesis of allyl amines

The first example of an additive-free decarboxylative coupling of cinnamic acid derivatives with formaldehyde and amines to afford the corresponding allyl amines is reported. This reaction is highly environmentally friendly because it was conducted in H2O and without any additives, releasing only CO2 and H2O as byproducts. This reaction showed a broad substrate scope including cyclic and acyclic amines and high functional group tolerance. Moreover, phenyl dienoic acid participated in this type of decarboxylative coupling reaction.

Excellent catalytic activity of magnetically recoverable Fe3O4–graphene oxide nanocomposites prepared by a simple method

An easy-to-prepare Fe₃O₄–graphene oxide nanocomposite which works well as a reusable catalyst for A³-coupling reactions.

Lanthanum loaded CuO nanoparticles: synthesis and characterization of a recyclable catalyst for the synthesis of 1,4-disubstituted 1,2,3-triazoles and propargylamines

A click and three component A³ coupling reactions were achieved by lanthanum loaded CuO NPs under ultrasonication. 1,4-Disubstituted 1,2,3-triazoles and propargylamines were synthesized in a short reaction time with high regioselectivity and yields.