Sonogashira reaction heterogeneous catalysts

Chouzier et al. (2004) have described the one-pot indole synthesis catalyzed by new heterogeneous bimetallic (Pd-Cu) catalysts via the Sonogashira C-C coupling reaction with up to 100% yield in short reaction times for the first time (Scheme 2.6). In all cases, a complete selectivity toward the indole compound is observed. The heterogeneous catalysts, while being deactivated during the extraction procedure in air, remain highly active and selective when used in a continuons manner. 

Palladium on charcoal (Pd/C) is a well-known heterogeneous source of Pd that is particularly valuable for industrial purposes because of its low cost, ready availabihty, and stabihty [90]. There have been several reports of the Sonogashira reaction using Pd/C as the metal source. These reactions displayed yields and conditions comparable to, or, in some cases, better than, the standard Pd catalysts (Table 9.5). 

Future avenues of research will focus on heterogeneous catalysis whereby highly active catalysts can be easily recycled and reused. Application has already begun in the established reactions such as Suzuki-Miyaura, Mizoroki-Heck and Sonogashira reactions. Over time it is expected that new C-H activation reactions will succumb to designed nanoparticle catalysis. Researchers in the field of total synthesis are... 

Ohtaka et al. [69] have introduced a linear polystyrene stabilized PdO nanoparticles (PS-PdO NPs) as an eco-friendly heterogeneous catalyst which was found to be highly efficient for Sonogashira reaction in H2O. The Sono-gashira cross-coupling between o-halo phenol and terminal alkyne produced benzofuran in the presence of PS-PdO NPs in presence of EtsN in water at 80°C for 20h (Scheme 48). 

Recently it has been observed that NCBs have been used as a support for heterogeneous catalyst due to its hollow core, mesoporous and ball-like structure. Park et al. [70] developed Pd(OAC)2 catalyst supported on NCBs and applied it for the synthesis of 2-substituted benzofuran from u-iodo phenol and various substituted terminal alkynes using Sonogashira cross-coupling reaction under copper and ligand-free condition. 

Sharma et al. reported on the synthesis and catalytic properties of bifunctional heterogeneous catalysts with basic and organometallic catalysts for efficient catalysis of two-step Sonogashira and Henry reactions [55]. With a solvent-assisted grafting method, two different catalytic groups— an organoamine and a palladium-organodiamine... 

F.X. (2010) Recyclable heterogeneous palladium catalysts in pure water sustainable developments in Suzuki, Heck, Sonogashira and Tsuji-Trost reactions. Adv. Synth. Catal., 352 (1), 33-79. 

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