A Catalytic Peterson-like Synthesis of Alkenyl Nitriles

A heterogeneous fluoride catalyst was found to enable the straightforward formation of alkenyl nitriles from the reaction of aldehydes and simple or substituted acetonitriles, in the presence of commercially available silazanes and in solvent-free conditions. The protocol afforded the products in good to excellent yields with selectivity values dependent on the nature of the substrates. It represents an alternative to classic approaches using stoichiometric strong bases, and the catalyst can be easily recovered and reused for consecutive cycles

Agarsenone, a Cadinane Sesquiterpenoid from <i>Commiphora erythraea</i>

Agarsenone (<b>1</b>), a new cadinane sesquiterpenoid, was isolated from the resin of <i>Commiphora erythraea.</i> The structures of <b>1</b> and its decomposition products agarsenolides (<b>2a</b> and <b>2b</b>) and myrrhone (<b>3</b>) were established by extensive NMR spectroscopic analysis. The absolute configuration of <b>3</b> and the relative and absolute configurations of <b>1</b> were assigned by comparison of experimental and calculated optical rotatory dispersion and electronic circular dichroism spectra

Origins of Stereoselectivity in Peptide-Catalyzed Kinetic Resolution of Alcohols

The origin of the stereoselectivity of the tetrapeptide-catalyzed kinetic resolution of <i>trans</i>-2-<i>N</i>-acetamidocyclohexanol is investigated by means of density functional theory calculations. Transition states for the functionalization of both (<i>R</i>,<i>R</i>) and (<i>S</i>,<i>S</i>) substrates were optimized considering all possible conformers. Due to the flexibility of the peptidic catalyst, a large number of transition states had to be located, and analysis of the geometries and energies allowed for the identification of the main factors that control the stereoselectivity

Theoretical Study of Mechanism and Stereoselectivity of Catalytic Kinugasa Reaction

The mechanism of the catalytic Kinugasa reaction is investigated by means of density functional theory calculations. Different possible mechanistic scenarios are presented using phenanthroline as a ligand, and it is shown that the most reasonable one in terms of energy barriers involves two copper ions. The reaction starts with the formation of a dicopper-acetylide that undergoes a stepwise cycloaddition with the nitrone, generating a five-membered ring intermediate. Protonation of the nitrogen of the metalated isoxazoline intermediate results in ring opening and the formation of a ketene intermediate. This then undergoes a copper-catalyzed cyclization by an intramolecular nucleophilic attack of the nitrogen on the ketene, affording a cyclic copper enolate. Catalyst release and tautomerization gives the final β-lactamic product. A comprehensive study of the enantioselective reaction was also performed with a chiral bis­(azaferrocene) ligand. In this case, two different reaction mechanisms, involving either the scenario with the two copper ions or a direct cycloaddition of the parent alkyne using one copper ion, were found to have quite similar barriers. Both mechanisms reproduced the experimental enantioselectivity, and the current calculations can therefore not distinguish between the two possibilities

Theoretical Study of Mechanism and Stereoselectivity of Catalytic Kinugasa Reaction

The mechanism of the catalytic Kinugasa reaction is investigated by means of density functional theory calculations. Different possible mechanistic scenarios are presented using phenanthroline as a ligand, and it is shown that the most reasonable one in terms of energy barriers involves two copper ions. The reaction starts with the formation of a dicopper-acetylide that undergoes a stepwise cycloaddition with the nitrone, generating a five-membered ring intermediate. Protonation of the nitrogen of the metalated isoxazoline intermediate results in ring opening and the formation of a ketene intermediate. This then undergoes a copper-catalyzed cyclization by an intramolecular nucleophilic attack of the nitrogen on the ketene, affording a cyclic copper enolate. Catalyst release and tautomerization gives the final β-lactamic product. A comprehensive study of the enantioselective reaction was also performed with a chiral bis­(azaferrocene) ligand. In this case, two different reaction mechanisms, involving either the scenario with the two copper ions or a direct cycloaddition of the parent alkyne using one copper ion, were found to have quite similar barriers. Both mechanisms reproduced the experimental enantioselectivity, and the current calculations can therefore not distinguish between the two possibilities

Enzyme-Like Catalysis via Ternary Complex Mechanism: Alkoxy-Bridged Dinuclear Cobalt Complex Mediates Chemoselective O‑Esterification over N‑Amidation

Hydroxy group-selective acylation in the presence of more nucleophilic amines was achieved using acetates of first-row late transition metals, such as Mn, Fe, Co, Cu, and Zn. Among them, cobalt­(II) acetate was the best catalyst in terms of reactivity and selectivity. The combination of an octanuclear cobalt carboxylate cluster [Co₄(OCOR)₆O]₂ (<b>2a</b>: R = CF₃, <b>2b</b>: R = CH₃, <b>2c</b>: R = ^<i>t</i>Bu) with nitrogen-containing ligands, such as 2,2′-bipyridine, provided an efficient catalytic system for transesterification, in which an alkoxide-bridged dinuclear complex, Co₂(OCO^<i>t</i>Bu)₂­(bpy)₂(μ₂-OCH₂-C₆H₄-4-CH₃)₂ (<b>10</b>), was successfully isolated as a key intermediate. Kinetic studies and density functional theory calculations revealed Michaelis–Menten behavior of the complex <b>10</b> through an ordered ternary complex mechanism similar to dinuclear metallo-enzymes, suggesting the formation of alkoxides followed by coordination of the ester

Waste Minimized Multistep Preparation in Flow of β‑Amino Acids Starting from α,β-Unsaturated Carboxylic Acids

An efficient protocol for the synthesis of β-amino acids starting from easily accessible α,β-unsaturated carboxylic acids based on the combination of two heterogeneous catalytic systems is reported. This multistep approach is based on the direct β-azidation of α,β-unsaturated carboxylic acids and subsequent azido group reduction performed in flow conditions. It has been demonstrated that the catalysts can be easily recovered and reused conserving its complete efficiency. The green metrics calculations proved the high environmental efficiency of the protocol characterized by very low waste production