Sonogashira coupling reaction ligand-free catalysts

The Sonogashira coupling reaction of terminal alkynes with aryl or vinyl halides is a useful tool for carbon—carbon bond formation, and has found wide employment in areas such as natural product synthesis, the pharmaceutical industry, and material sciences. Novel recyclable Pd catalysts with fluorous ponytails in the ligand 2,2 -bipyridine were reported in a copper-free Pd-catalyzed Sonogashira reaction in a fluorous biphasic system (FBS) (Equation 4.19). The catalysts are only soluble in perfluorinated solvents at room temperature [41],... 

For the copper-free Sonogashira reaction, the mechanistic study reported in this thesis revealed that, just like in other cross-coupling reactions (i.e. Stille, Negishi), there are several competing reaction pathways and a change on the reaction conditions (e.g. solvent, ligands, substrates, base) might favor one over the other ones. Moreover, a new mechanism in which the acetylide (formed by deprotonation of the alkyne) directly reacts with the catalyst was also proposed. 

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. 

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