Reductive Aza-Pauson-Khand Reaction of Nitriles

Access to Polysubstituted Pyrimidin-2-ones by Pd-Catalyzed [2 + 2 + 2] Cycloaddition of Alkyne-Tethered Malononitriles and Isocyanates

Transition-metal-catalyzed [2 + 2 + 2] cycloaddition reactions of alkynes, nitriles, and other π partners have been recognized as economic strategies to assemble aza-six-membered rings, but access to pyrimidin-2-ones is not disclosed. Herein, we report a palladium-catalyzed [2 + 2 + 2] cycloaddition of 1,3-diyne-substituted malononitriles and isocyanates for the construction of polysubstituted pyrimidin-2-ones. This reaction features a broad substrate scope and moderate to high yields. Conjugated pyrimidin-2-one acting as a fluorophore showcased potential as a fluorescent chemosensor for Fe(III) detection.

Development of Controllable Hetero-Pauson-Khand Polymerization to Functional Stimuli-Responsive Poly(γ-lactam)s

Polymers containing lactam structures play a crucial role in both natural biological systems and human life, and their synthesis, functions and applications are of utmost importance for biomimetics and the creation of new materials. In this study, we developed an efficient heterogeneous Pauson-Khand polymerization (h-PKP) method for the controlled synthesis of main-chain poly(γ-lactam)s containing α, β-unsaturated γ-lactam functionalities using readily available internal alkynes and imines. The molecular weights of the resulting poly(N-Ts/γ-lactam)s can be precisely controlled by adjusting the ratio of phenyl formate and nickel. These polymers exhibit high solid-state luminescence and demonstrate rapid and sensitive dual responsiveness to light and acid stimuli. They further demonstrate strong reactive oxygen species (ROS) generation capability. The unique dual-emission peaks observed in poly(N-H/γ-lactam)s obtained through post-treatment under acidic conditions demonstrate a mechanism of aggregation-induced intermolecular excited-state proton transfer specific to lactam structures. The efficient one-pot synthetic method for poly(γ-lactam) provides a novel strategy for constructing polymers with γ-lactam structures in the main chain and the simple and efficient post-modification method offer a versatile toolbox for functionalizing poly(γ-lactam)s to expand their potential applications.

Pd/Cu Dual Metal-Catalyzed Regioselective [2 + 2 + 2] Cycloaddition of Malononitriles with Alkynes to Densely Substituted Pyridines

Transition metal-catalyzed [2 + 2 + 2] cycloaddition of nitriles and two alkynes is an efficient method for assembling pyridines. However, examples employing palladium catalysis have rarely been disclosed, and the processes of reactivity and selectivity remain unclear. We report here a palladium/copper dual metal-catalyzed [2 + 2 + 2] cycloaddition of diynyl-tethered malononitriles and terminal alkynes to synthesize densely substituted pyridines. This method features a good substrate scope, synthetically useful yields, and perfect regioselectivity. The derivatization of the pyridine products demonstrates the potential application of this method in synthesizing heterocycles and as ligands in photocatalysis. Preliminary mechanistic studies suggest that the reaction undergoes aza-oxidative cycloaddition of Pd(0) with nitrile and alkyne, followed by alkyne insertion and reductive elimination. The presence of copper is crucial to its reactivity and regioselectivity.

Light-Driven Three-Component Carbonylation of Aryl Halides Using Abundant Metal Carbonyl

Carbonyl compounds are widely found in various pharmaceutical intermediates and synthetic precursors. Herein we report a simple light-driven three-component aryl halide process for synthesizing a variety of carbonylation products, utilizing Co2(CO)8 as an abundant solid carbonyl source, in good to excellent yields. The products can easily be subjected to further functionalization in synthesis. Mechanism studies indicated that this reaction is enabled by aryl radical generation and the subsequent CO insertion, alkene insertion, and protonation process.