Glycerol-derived solvents as non-innocent reaction media for additive-free Pd- and Au-catalysed transformations

Solvents represent a key issue in sustainable organic synthesis, as alternatives to the toxic, flammable and non-renewable volatile organic compounds are constantly being sought.1 Notably, some of these novel unconventional solvents can play an active role in the reaction, thus replacing a normally required reagent or catalyst. Here, we propose the application of a family of eco-compatible solvents, based on glycerol derivatives,2 for transition metal-catalysed reactions. The use of glycerol-derived ionic liquids with a carboxylate anion allows to perform Pd-catalysed direct C–H arylations of thiophene derivatives, avoiding super-stoichiometric amounts of base, for the synthesis of conjugated scaffolds for optoelectronics and imaging. On the other hand, Au(I) catalysis is pivotal to the synthesis of complex molecular architectures, but expensive Ag co-catalysts are generally required, which can also negatively interfere with the reaction.3 Here we show that glycerol mono- and diethers, when used as solvents, are effective activators for Au(I) pre-catalysts, enabling Ag-free Au(I) catalysis.