Triazine‐Triazole Conjugates as Potent Ligands for Cu–Catalyzed Sonogashira Reaction

Abstract

Triazine Triazole conjugates (TT) were developed as efficient ligand system for CuSO 4 ·5H 2 O catalyzed Sonogashira and decarboxylative cross-coupling reaction. This new protocol showed good compatibility with a broad range of substitutents and afforded moderate to excellent yields. TT ligands are rapid constructed and highly modular electronically and sterically.Alkyne products obtained via Sonogashira reaction widely used in the most diverse areas of chemistry, such as dyes, sensors, electronics, polymers, guest-host constructs, natural products and heterocycle synthesis. [1][2] The classic Sonogashira coupling procedures relied on palladium as catalyst, and originally copper iodide was added to facilitate the transmetallation of alkynyl moiety. [3] The high cost of palladium salts, requirement of copper co-catalyst, high oxophillicity associated with phosphine ligands have rendered Pd unpopular, particularly for large-scale reactions. For these reasons, much recent effort has been made to achieve the Sonogashira reaction in absence of the expensive noble metal palladium and using more sustainable metals like Fe, [4] Ni [5] and Cu. [6] Among them, copper is a potent alternative to the palladium in a large variety of CÀN, CÀO, and CÀC cross-coupling reactions. These Cu-catalyzed reactions are robust, can be performed with simple ligands, making them highly attractive to these engaged in the synthesis of complex molecular architecture. [7] Despite of the early success of PPh 3 , [6a-c] a range of commercial available ligands including EN, [6d] DMEDA, [6e-f] DABCO, [6g] pyrimidines, [6h] acac, [6i] rac-BINOL, [6j] salicylic acid [6k] and methionine [6l-m] were found to accelerate the copper-catalyzed Sonogashira reaction. A key advantage of these simple ligands for copper over some others was the easily access to bidentated coordination mode, and consequently stabilized catalytic active species. The steric and electronic optimization on these simple molecules also enhanced the activity of copper catalyst. N,N'dibenzyl-BINAM, [6n] diphenylpropane-1,3-dione, [6o] N,N'-di-8-quinolylamidinates, [6p] N,N-dimethylglycine [6q] were prepared ac- [a]

Copper-catalyzed Sonogashira reactions: advances and perspectives since 2014

“…Wang and co-workers utilized triazine triazole conjugates (TT) as ligand system for copper catalyzed Sonogashira and decarboxylative cross-coupling reaction. 30 For the copper-catalyzed Sonogashira reaction, TT conjugates were identified as effective N,N′ donor ligands. The electron-donating groups on heterocyclic rings were found to be adverse for enhancing the catalytic efficiency of TT ligands in ligand effect tests.…”