Silver-catalyzed three-component coupling

Li and coworkers have reported a novel silver-catalyzed, three-component coupling of an aldehyde, an amine, and an alkyne, and the first example of a direct addition of a silver acetylide to an aldehyde to produce propargylic alcohols (Scheme 1.41).103-105 Treatment of an aldehyde with a silver halide and secondary amine gave propargylic amines in good yields in organic solvent, water, or ionic liquids. The proposed mechanism suggests addition of a silver acetylide to the iminium ion formed in situ. 

In a closely related reaction, Li et al.101 devised a silver-catalyzed three-component coupling between aldehydes, alkynes, and amines. This transformation was really efficient in water and in an ionic liquid, although both required overnight heating at 100°C (Table 10.6). In this reaction, a silver acetylide that was sufficiently nucleophilic to add to the iminium ion that formed by condensation of the amine on the aldehyde was certainly produced.8... 

Supported versions of such silver-catalyzed, three-component couplings have been recently reported. Silver oxide on multiwall carbon nanotubes or on alumina,102 as well as silver-doped zeolites,103 proved to be efficient and reusable catalysts for such coupling reactions. In the former, water was used as solvent, while in the latter, no solvent was required, making it a truly green process. 

The Garner group has developed a silver acetate/triphenylphosphine (10mol%) catalyzed one-pot three-component coupling (Scheme 2.20) of aldehydes 72, methyl acrylate (27), and dimethyl-2-aminomalonate (73,2 equiv).39 Notably, both aliphatic and aromatic aldehydes may participate in the reaction and yields up to 95% can be achieved. 

Li and co-workers374,374a reported the three-component coupling reaction of an aldehyde, an amine, and a terminal alkyne catalyzed by a silver salt in water. Of various precatalysts examined, water-insoluble silver iodide gave the highest yields of the propargyl amines 452 (Scheme 137). The reaction probably proceeds via attack of a silver acetylide, generated in situ from the silver salt and the alkyne, to the iminium ion derived from the aldehyde and the... 

The aldehyde component has also been replaced by diethyl formylphosphonate hydrate in the silver-catalyzed synthesis of V-PMP-protected a-aminopropargylphospho-nates [139] and by 2-oxoacetic acid [140] or glyoxylic acid [141] in copper-catalyzed microwave-assisted decarboxyla-tive three-component couplings. In addition, glyoxylic acid has been coupled with amines and alkynes in the gold-catalyzed synthesis of butenolides (see Scheme 3.48) [121]. 

X. Zhou, Y. Lu, L.-L. Zhai, Y. Zhao, Q. Liu, W.-Y. Sun, RSC Adv. 2013, 3, 1732-1734. Propargylamines formed from three-component coupling reactions catalyzed by silver oxide nanoparticles. 

Meyers Al (1974) Heterocycles in organic synthesis. Wiley-lnterscience, New York Safaei-Ghomi J, Ghasemzadeh MA, Kakavand-Qalenoei A (2012) Cul-nanoparticles-cat-alyzed one-pot synthesis of benzo[6]furans via three-component coupling of aldehydes, amines and alkyne. J Saud Chem Soc. http //dx.doi.Org/10.1016/j.jscs.2012.07.010 Yu M, Lin M, Han C, Zhu L, Li C-J, Yao X (2010) Ligand-promoted reaction on silver nanoparticles phosphine-promoted, silver nanoparticle-catalyzed cyclization of 2-(l-hy-droxy-3-arylprop-2-ynyl)phenols. Tet Lett 51 6722-6725... 

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