Halogen atom transfer radical cyclization of N-allyl-N-benzyl-2,2-dihaloamides to 2-pyrrolidinones, promoted by Fe0-FeCl3 or CuCl-TMEDA

Microwave-Assisted Atom Transfer Radical Cyclization in the Synthesis of 3,3-Dichloro-γ- and δ-Lactams from N-Alkenyl-Tethered Trichloroacetamides Catalyzed by RuCl2(PPh3)3 and Their Cytotoxic Evaluation

An expeditious synthesis of γ- and δ-lactams from tethered alkenyl trichloroacetamides in the presence of 5% of RuCl2(PPh3)3 is reported. In this investigation we have demonstrated that microwave activation significantly enhances reaction rates, leading to the formation of the corresponding lactams in yields ranging from good to excellent. Thus, we have been able to prepare a wide range of lactams, including indole and morphan bicyclic scaffolds, where the corresponding reactions were completely diastereoselective. This process was successfully extended to α,α-dichloroamides without affecting either their yield or their diastereoselectivity. Some of the lactams prepared in this work were evaluated for their hemolytic and cytotoxic responses. All compounds were found to be non-hemolytic at the tested concentration, indicating their safety profile in terms of blood cell integrity. Meanwhile, they exhibited interesting cytotoxicity responses that depend on both their lactam structure and cell line. Among the molecules tested, γ-lactam 2a exhibited the lowest IC50 values (100-250 µg/mL) as a function of its cell line, with promising selectivity against squamous carcinoma cells (A431) in comparison with fibroblasts (3T3 cell line).

Photoredox catalysis in the synthesis of γ- and δ-lactams from N-alkenyl trichloro- and dichloroacetamides

The first blue light-mediated synthesis of γ- and δ-lactams from trichloroacetamides is reported in the presence of fac-Ir(ppy)₃. Unlike previous works, these reactions are achieved under an air atmosphere with non-anhydrous solvents and even in water. Moreover, we have demonstrated that the solvent can be the hydrogen donor in the radical process which opens up new insights into these radical transformations and the reaction mechanisms involved.

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C-N, C-O and C-S bond forming reactions, and later widely employed in C-C cross-coupling reactions with C(sp3), C(sp2) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.

Secondary Products from Intramolecular Cycloadditions of Azidoalkyl Enol Ethers and Azidoalkyl Vinyl Bromides: 1-Azadienes, Their Reactions with Diphenylketene, and Radical Cyclizations To Form Bi- and Tricyclic Lactams

Azidoalkyl enol ethers undergo intramolecular 1,3-dipolar cycloaddition to generate stable triazolines; in contrast, the cycloadducts formed by heating analogous azidoalkyl vinyl bromides are unstable with respect to elimination of N₂ and HBr, affording 1-azadienes (2-alkenyl cyclic imines). These primary products may be isolated or treated directly with diphenylketene to produce bi- and tricyclic 3,4-dihydropyridin-2(1H)-ones; similar ring systems may also be produced from the azadienes by N-acylation and radical cyclization.

Synthesis of substituted γ- and δ-lactams based on titanocene(iii)-catalysed radical cyclisations of trichloroacetamides

Straightforward synthesis of dehalogenated γ- and δ-lactams based on a Cp₂TiCl-catalysed radical cyclisation of trichloroacetamides under mild conditions.

Towards the development of highly active copper catalysts for atom transfer radical addition (ATRA) and polymerization (ATRP)‡

Fundamentals of copper catalyzed atom transfer radical addition (ATRA) and mechanistically similar polymerization (ATRP) were discussed. Special emphasis was placed on structural characterization and electrochemical properties of copper complexes. Recent advances in the development of highly active copper complexes for both processes were also reviewed. It was found that electron-donating groups (methoxy and methyl in the 4 and 3,5 positions, respectively) of the pyridine rings in tris(2-pyridylmethyl)amine (TPMA) ligand, significantly increase the catalytic activity in copper mediated ATRA/ATRP.

Regiochemistry of Copper(I)-Mediated Cyclization Reactions of Halo-dienamides

Reaction of 2-substituted dienamides with catalytic amounts of copper halide/tripyridylamine (TPA) furnishes either 5-exo or 6-endo products with the outcome dependent upon the radical initiating unit. Reaction of 3-substituted dienamides produces beta-lactams via a 4-exo cyclization with termination of the reaction occurring via either halogen atom transfer, trapping with oxygen, elimination, or radical-radical coupling depending upon the diene.

Solid-Supported Copper Catalysts for Atom-Transfer Radical Cyclizations: Assessment of Support Type and Ligand Structure on Catalyst Performance in the Synthesis of Nitrogen Heterocycles

A range of solid supported pyridinemethanimine 9-11 and polyamine 12-15 ligands have been prepared on silica, polystyrene, and JandaJel supports. The CuCl and CuBr complexes of these supported ligands have been used to assess both the effect of the ligand type and the nature of the support upon a representative range of copper-mediated atom transfer 5-exo-trig 6, 24-25, 5-exo-dig 26, 4-exo-trig 28, and 5-endo-trig 27, 38 radical cyclizations to give nitrogen heterocycles. In addition, the effect of the nature of the support on the stereochemical outcome of the 5-exo cyclization of 25 has been probed. Generally, it was found that the type of support (e.g., polystyrene, silica, or JandaJel) had very little effect upon the efficiency and selectivity of the processes but that the nature of the ligand type immobilized was the important factor. Thus, the 5-exo cyclization of 6 and 24-26 proceeded more rapidly with the PMI ligands 9-11, whereas 4-exo cyclizations 28 and 5-endo radical polar crossover reactions 27 and 38 proceeded more efficiently with the JJ-TEDETA ligand 15. The efficiency of the supported ligands was also compared to their solution counterparts 4 and 5. The reusability of P-PMDETA ligand system 13 was assessed in the cyclization of 6.

Kinetic evidence for hydrophobically stabilized encounter complexes formed by hydrophobic esters in aqueous solutions containing monohydric alcohols

The pH-independent hydrolysis of four esters, p-methoxyphenyl 2,2-dichloroethanoate (1a), p-methoxyphenyl 2,2-dichloropropanoate (1b), p-methoxyphenyl 2,2-dichlorobutanoate (1c), and p-methoxyphenyl 2,2-dichloropentanoate (1d), in dilute aqueous solution has been studied as a function of the molality of added cosolutes ethanol, 1-propanol, and 1-butanol. The rate constants for the neutral hydrolysis decrease with increasing cosolute concentration. These kinetic medium effects respond to both the hydrophobicity of the ester and of the monohydric alcohol. The observed rate effects were analyzed using both a thermodynamic and a kinetic model. The kinetic model suggests a molecular picture of a hydrophobically stabilized encounter complex, with equilibrium constants K(ec) often smaller than unity, in which the cosolute blocks the reaction center of the hydrolytic ester for attack by water. The formation of these encounter complexes leads to a dominant initial-state stabilization as follows from the thermodynamic model. Decreases in both apparent enthalpies and entropies of activation for these hydrolysis reactions correspond to unfavorable enthalpies and favorable entropies of complexation, which confirms that the encounter complexes are stabilized by hydrophobic interactions.