Intramolecular Carbolithiation of Heterosubstituted Alkynes: An Experimental and Theoretical Study

Nickel-Catalyzed Intramolecular Hydrosilylation of Alkynes: Embracing Conventional and Electrochemical Routes

Nickel-catalyzed intramolecular hydrosilylation can be efficiently achieved with high regio- and stereoselectivities through two distinct methodologies. The first approach utilizes a conventional method, involving the reduction of nickel salt (NiBr2-2,2'-bipyridine) using manganese metal. The second method employs a one-step electrochemical reaction, utilizing the sacrificial anode process and NiBr2bipy catalysis. Both methods yield silylated heterocycles in good to high yields through a syn-exo-dig cyclization process. Control experiments and molecular electrochemistry (cyclic voltammetry) provided further insights into the reaction mechanism.

Triton B-promoted regioselective intramolecular addition of enolates to tethered ynamides for the construction of 8-membered O-heterocycles

Benzo-1,5 dioxocines have been synthesized via unique ynamides tethered to propargylic ethers. Triton B allowed a proximal enol addition on the N-allenamide creating shelf-stable 8-membered-O-heterocycles with a broad functional group tolerance.

Nickel-Catalyzed Electrochemical Cyclization of Alkynyl Aryl Iodide and the Domino Reaction with Aldehydes

An intramolecular carbometallation of a triple bond promoted by electrochemistry and mediated by nickel catalysis is described. This domino process transforms various aryl halides bearing a propargyl chain into substituted heterocycles in one single operation, with high stereoselectivities and in good to high yields. This reaction, characterized by a cyclic voltammetry set of experiments, proceeds following a syn-exo-dig cyclization process. When run at 80 °C, vinylbenzofuranes that are suitable substrates for cycloaddition reactions are obtained.

Conformational Isomerism of 3-Chalcogenomethyl-N-Methyl-2-Pyrrolidinones: Insights from NMR Spectroscopy and Molecular Modeling

A conformational analysis of N-methyl-2-pyrrolidinone 3-substituted by methoxyl, thiomethoxyl, and selenomethoxyl is reported by means of ¹H nuclear magnetic resonance spectroscopy and electronic structure calculations. The five-membered ring has an envelope conformation with the α-carbonyl substituent being able to assume two positions: pseudo-axial and pseudo-equatorial. In vacuum, the calculations pointed to the pseudo-axial conformer as the most stable one, and this preference increases with the size of the substituent and a decrease in its electronegativity. Natural bond orbital analysis evidenced the importance of electron delocalization on the stability, and a principal component of analysis (PCA) plot of the hyperconjugative interactions revealed the main ones. Steric and electrostatic effects were also investigated by energy decomposition analysis.