Au-complex containing phosphino and imidazolyl moieties as a bi-functional catalyst for one-pot synthesis of pyridine derivatives

Synthesis of Nitrogen-Containing Heterocyclic Scaffolds through Sequential Reactions of Aminoalkynes with Carbonyls

Sequential reactions of aminoalkynes represent a powerful tool to easily assembly biologically important polyfunctionalized nitrogen heterocyclic scaffolds. Metal catalysis often plays a key role in terms of selectivity, efficiency, atom economy, and green chemistry of these sequential approaches. This review examines the existing literature on the applications of reactions of aminoalkynes with carbonyls, which are emerging for their synthetic potential. Aspects concerning the features of the starting reagents, the catalytic systems, alternative reaction conditions, pathways and possible intermediates are provided.

Aurophilic Interactions of Dimeric Bisphosphine Gold(I) Complexes Pre-Organized by the Structure of the 1,5-Diaza-3,7-Diphosphacyclooctanes

The dimeric gold(I) chloride and gold(I) iodide complexes ([L2Au]Cl2 and L2AuI2) on the scaffold of the cyclic bisphosphine, namely 1,5-diaza-3,7-diphosphacyclooctane containing α-phenylbenzyl (benzhydryl) substituents at the nitrogen atoms, were synthesized. The obtained complexes were isolated as white crystalline powders. The single crystal XRD of the obtained complexes revealed the strong aurophilic interactions between two gold(I) atoms with the Au…Au distance values of 2.9977(6) and 3.1680(5) Å. The comparison of the gold complexes, based on the N,N-diaryl- and N,N-dibenzhydryl substituted 1,5-diaza-3,7-diphosphacyclooctanes, allowed to reveal the strong impact of the initial heterocycle conformation on the realization of the aurophilic interactions, where the geometry of N,N-dibenzhydryl substituted 1,5-diaza-3,7-diphosphacyclooctane, is pre-organized for the intramolecular aurophilic interactions of the complexes. The obtained complexes exhibit a bluish-green phosphorescence (λem 505 (-Cl) and 530(-I)) in the solid state at room temperature, originated by the metal-halide centered transitions, which was confirmed by the TDDFT calculations. It was found that the aurophilic interactions are realized in the ground and in the triplet excited states of the complexes. The slighter change of the geometry of the N,N-dibenzhydryl substituted gold(I) iodide complexes, under the transition from the ground state to the excited state, in comparison with their N,N-diaryl substituted analogues, results in the reduced values of the Stokes shift of luminescence (ca. 150 nm vs. 175 nm).

1,2,3-Triazole based ligands with phosphine and pyridine functionalities: synthesis, PdII and PtII chemistry and catalytic studies

This manuscript describes the syntheses of pyridine appended triazole-based mono- and bisphosphines, [o-Ph₂P(C₆H₄){1,2,3-N₃C(Py)C(H)}] (2), [o-Br(C₆H₄){1,2,3-N₃C(Py)C(PPh₂)}] (3), [C₆H₅{1,2,3-N₃C(Py)C(PPh₂)}] (4), [Ph₂P(C₆H₄){1,2,3-N₃C(Py)C(PPh₂)}] (5) and [3-Ph₂P-2-{1,2,3-N₃C(Ph)C(PPh₂)}C₅H₃N] (6), their palladium and platinum chemistry and catalytic applications. These ligands upon treatment with [M(COD)Cl₂] (M = Pd or Pt) yielded complexes with different coordination modes, depending on the reaction conditions. Both κ²-P,N and κ²-P,P coordination modes were observed in many of the complexes indicating the ambidentate nature of these ligands. Monophosphine 2 in the presence of a base afforded rare fused-5,6-membered PCN pincer complexes [MCl{o-Ph₂P(C₆H₄){1,2,3-N₃C(Py)C(H)}}-κ³-P,C,N] (7, M = Pd; 8, M = Pt), whereas the reactions of 4 with [M(COD)Cl₂] (M = Pd, Pt) produced κ²-P,N chelate complexes [MCl₂{C₆H₅{1,2,3-N₃C(Py)C(PPh₂)}-κ²-P,N}] (9, M = Pd; 10, M = Pt). Similar reactions of 5 and 6 resulted in κ²-P,P chelate complexes [MCl₂{{3-Ph₂P-2-{1,2,3-N₃C(Ph)C(PPh₂)}C₅H₃N}-κ²-P,P}] (11, M = Pd; 12, M = Pt) and [MCl₂{3-Ph₂P-2-{1,2,3-N₃C(Ph)C(PPh₂)}C₅H₃N}-κ²-P,P}] (13, M = Pd; 14, M = Pt), respectively. The palladium(II) complexes have shown excellent catalytic activity in the α-alkylation reaction of acetophenone derivatives.

Cu-Catalyzed Pyridine Synthesis via Oxidative Annulation of Cyclic Ketones with Propargylamine

A Cu-catalyzed, easily scalable one-pot synthesis of fused pyridines by the reaction of cyclic ketones with propargylamine is described. The protocol was optimized based on the results of more than 30 experiments. The highest product yields were achieved in i-PrOH as a solvent in the presence of 5.0 mol % CuCl₂ in air. In contrast to the well-known Au-catalyzed protocol, our procedure is "laboratory friendly", cost-effective, and suitable for preparing dozens of grams of fused pyridine-based building blocks and does not require a high-pressure autoclave technique. Decreasing the catalyst amount in the reaction to 1.25 mol % CuCl₂ provided a yield comparable to that achieved with 5 mol % catalyst, though a longer reaction time was required. A plausible reaction mechanism was proposed. The scope and limitation of the reaction were studied using 24 different cyclic ketones as starting materials. The fused pyridine yield decreased among cyclic ketones in the following order: six-membered ≫ eight-membered > five-membered ∼ seven-membered. The elaborated reaction conditions demonstrated tolerance to a number of protective functional groups in ketone such as ester, tert-butoxycarbonyl (Boc)-protected amine, and acetal moieties.