Heterogeneous intermolecular hydroamination of terminal alkynes with aromatic amines

Green imine synthesis from amines using transition metal and micellar catalysis

Imines are a versatile class of chemicals with applications in pharmaceuticals and as synthetic intermediates. While imines are conventionally synthesized via aldehyde-amine condensation, their direct preparation from amines can avoid the need for the independent preparation of the aldehyde coupling partner and associated constraints with regard to aldehyde storage and purification. The direct preparation of imines from amines typically utilizes transition metal catalysis and is often well-aligned with green chemistry principles. This review provides a comprehensive overview of transition metal catalysed imine synthesis, with a particular focus on the copper-catalyzed oxidative coupling of amines. The emerging application of micellar catalysis for imine synthesis is also surveyed due to its potential to avoid the use of hazardous solvents and intensify these reactions through reduced catalyst loadings and locally increased reactant concentrations. Future directions relating to the confluence of these two areas are proposed towards the more sustainable preparation of imines.

Fullerene C60 promoted photochemical hydroamination reactions of an electron deficient alkyne with trimethylsilyl group containing tertiary N-alkylbenzylamines

C60-promoted photoaddition reactions of both trimethylsilyl- and a variety of alkyl group containing tertiary benzylamines (i.e., N-α-trimethylsilyl-N-alkylbenzylamines) with dimethyl acetylenedicarboxylate (DMAD) were carried out to explore the synthetic utility of trimethylsilyl group containing tertiary amines as a substrate in the photochemical hydroamination reactions with dimethyl acetylenedicarboxylate (DMAD). The results showed that photoreactions of all the trimethylsilyl containing N-alkylbenzylamines with DMAD, under an O2-purged environment, produced non-silyl containing enamines efficiently through a pathway involving addition of secondary amines to DMAD, the former of which are produced by hydrolytic cleavage of in situ formed iminium ions. Exceptionally, five-membered N-heterocyclic rings, pyrroles, could be produced competitively in photoreaction of bulky alkyl (i.e., tert-butyl) group substituted benzylamines through a pathway involving 1,3-dipolar cycloaddition of azomethine ylides to DMAD. Furthermore, C60-sensitized photochemical reactions of non-silyl containing benzylamines with DMAD under oxygenated conditions took place in a less efficient and non-regioselective manner to produce enamine photoadducts. The observations made in this study show that regioselectivity of C60-promoted photochemical reactions of N-α-trimethylsilyl-N-alkylbenzylamines, leading to formation of secondary amines, can be controlled by the presence of the trimethylsilyl group, and that these trimethylsilyl containing tertiary amines can serve as a precursor of secondary amines for hydroamination reactions with a variety of electron deficient acetylenes.

Catalysis and regioselectivity in hydrofunctionalization reactions of unsaturated carbon bonds. Part II. Hydroamination

This review continues consideration of the regioselectivity problem in the catalyzed hydrofunctionalization of unsaturated organic compounds and addresses hydroamination of unsaturated hydrocarbons. Particular parts of the review deal with reactions of alkenes, alkynes, allenes and dienes. It is shown that the selectivity of hydroamination depends on the natures of the reactants and the catalyst. Conditions of the reactions are described; in some cases, reaction mechanisms are discussed. Reactions for which divergent regioselectivity is possible are noted.

The bibliography includes 249 references.

Dedicated to the memory of V.V.Markovnikov.

MAu2GeS4-Chalcogel (M = Co, Ni): Heterogeneous Intra- and Intermolecular Hydroamination Catalysts

High surface area macroporous chalcogenide aerogels (chalcogels) MAu₂GeS₄ (M = Co, Ni) were prepared from K₂Au₂GeS₄ precursor and Co(OAc)₂ or NiCl₂ by one-pot sol-gel metathesis reactions in aqueous media. The MAu₂GeS₄-chalcogels were screened for catalytic intramolecular hydroamination of 4-pentyn-1-amine substrate at different temperatures. 87% and 58% conversion was achieved at 100 °C, using CoAu₂GeS₄- and NiAu₂GeS₄-chalcogels respectively, and the reaction kinetics follows the first order. It was established that the catalytic performance of the aerogels is associated with the M²⁺ centers present in the structure. Intermolecular hydroamination of aniline with 1-R-4-ethynylbenzene (R = -H, -OCH₃, -Br, -F) was carried out at 100 °C using CoAu₂GeS₄-chalcogel catalyst, due to its promising catalytic performance. The CoAu₂GeS₄-chalcogel regioselectively converted the pair of substrates to respective Markovnikov products, (E)-1-(4-R-phenyl)-N-phenylethan-1-imine, with 38% to 60% conversion.

Factors influencing the photocatalytic hydroamination of alkynes with anilines catalyzed by supported gold nanoparticles under visible light irradiation

The hydroamination of alkynes with amines is successfully driven by visible-light when using AuNPs on metal oxide supports as plasmonic photocatalysts.

Hydroamination of terminal alkynes with secondary amines catalyzed by copper: regioselective access to amines

A simple and convenient copper-catalyzed hydroamination of arylacetylenes with secondary amines has been performed giving a simple access to aliphatic amines after reduction of the hydroaminated products (E-enamines).

Development of new hydrogenations of imines and benign reductive hydroaminations: zinc triflate as a catalyst

The hydrogenation of imines to amines in the presence of catalytic amounts of zinc triflate has been demonstrated for the first time. In addition, an efficient procedure for the reductive hydroamination of alkynes to amines is presented using zinc triflate as a catalyst precursor. In both protocols a variety of different functional groups are tolerated, and the reactions proceed smoothly in high yields.

A new facile synthesis of 3-amidoindole derivatives and their evaluation as potential GSK-3beta inhibitors

3-Amidoindoles were synthesized from commercially available arylhydrazines and propargylamines over Zn-salt mediated one pot procedure in excellent regioselectivity and up to 94% yield.

Efficient and selective telomerization of 1,3-butadiene with diols catalyzed by palladium-carbene complexes

The selective telomerization of 1,3-butadiene with seven different linear and cyclic diols proceeds in the presence of in situ generated palladium carbene catalysts. By applying optimized reaction conditions, including very low metal loadings (2-10 ppm), excellent catalyst turnover numbers (>250,000) and good chemoselectivities are observed with respect to the mono-octadienyl ether derivatives. This protocol allows the efficient preparation of unsaturated alcohols, which are useful for various applications.

General zinc-catalyzed intermolecular hydroamination of terminal alkynes

Catalytic hydroaminations are one of the most sustainable C-N bond-forming processes as a result of 100% atom economy and the availability of substrates. Here, it is shown that the intermolecular hydroamination of terminal alkynes with anilines proceeds smoothly in the presence of catalytic amounts of zinc triflate, an easily available and inexpensive zinc salt. Amination and subsequent reduction with NaBH3CN gives a variety of secondary and tertiary amines in up to 99% yield and with over 99% Markovnikov regioselectivity. Moreover, difficult functional groups such as nitro and cyano substituents are tolerated by the homogeneous catalyst.

An efficient reusable silver-exchanged tungstophosphoric acid heterogeneous catalyst for solvent-free intermolecular hydroamination of alkynes

Hydroamination of alkynes with both aromatic and aliphatic amines proceeds efficiently in the presence of silver-exchanged tungstophosphoric acid (AgTPA) catalyst under solvent-free conditions to afford ketimines in excellent yields.

The catalytic hydroamination of alkynes

Catalytic additions of ammonia or primary and secondary amines to non-activated alkenes and alkynes are called hydroaminations. These reactions of fundamental simplicity represent the most atom efficient processes for the formation of amines, enamines and imines, which are important bulk and fine chemicals or building blocks in organic synthesis. Consequently, the development of corresponding hydroamination reactions has received much attention and great progress has been achieved in the case of catalytic hydroaminations of alkynes over the past four years. To illustrate this progress, this tutorial review will mostly focus on recent developments in the field of intermolecular hydroamination of alkynes that appeared in the literature between the end of 2002 and October 31, 2006.