An Alternative to Nitromethane as Solvent: The Promoting Influence of Nitro-Functionalized Imidazolium Salts for Synthesis and Catalysis

Nitromethane, a volatile and toxic organic compound, is commonly used as solvent for organic and catalytic reactions. In order to find an alternative for this specific nitro-containing organic solvent, the performance of some nitro-functionalized imidazoli- um salts such as 1-methyl-3-(4-nitrobenzyl)imidazoli- um hexafluorophosphate, 1-methyl-3-(4-nitrobenz- A tetrafluoroborate, 1-methyl-3-(4-ni- trobenzyl)imidazolium bis(trifluoromethanesulfonyl)- A and 1,2-dimethyl-3-(4- nitrobenzyl)imidazoli- um hexafluorophosphate, was examined in some reactions including trimethylsilylation of alcohols with hexamethyldisilazane, ring-opening reactions of 2-aryl-3,4-dihydropyrans with thiophenols or thiols, and a copper- mediated oxidative coupling of al- kynes. As expected, these imidazolium salts can indeed replace nitromethane in these reactions. Par- ticularly, the imidazolium salt along with the metal catalyst, if involved, can be easily recovered and reused without significant loss of activity. The use of these nitro-functionalized imidazolium salts as alter- native solvents for nitromethane not only confers a green aspect to the reaction system, but also facili- tates a rational design of a catalytic system with the concept of green chemistry.