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

Abstract

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 imidazolium salts such as 1-methyl-3-(4-nitrobenzyl)imidazolium hexafluorophosphate, 1-methyl-3-(4-nitrobenz-A C H T U N G T R E N N U N G yl)imidazolium tetrafluoroborate, 1-methyl-3-(4-nitrobenzyl)imidazolium bis(trifluoromethanesulfonyl)-A C H T U N G T R E N N U N G amide and 1,2-dimethyl-3-(4-nitrobenzyl)imidazolium 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 alkynes. As expected, these imidazolium salts can indeed replace nitromethane in these reactions. Particularly, 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 alternative solvents for nitromethane not only confers a green aspect to the reaction system, but also facilitates a rational design of a catalytic system with the concept of green chemistry.

Chiral Copper(II) Phosphate Catalyzed Enantioselective Synthesis of Isochromene Derivatives by Sequential Intramolecular Cyclization and Asymmetric Transfer Hydrogenation of o‐Alkynylacetophenones

“…When (S)-5 a was treated with an excess amount of boron trifluoride etherate in the presence of pbromobenzenethiol in CH 2 Cl 2 , the chiral sulfide 7 was obtained in 77 % yield with 91 % chirality transfer. [16] The absolute configuration of the major enantiomer of 7 was determined to be R. [17] It was confirmed that the present reaction proceeded with inversion of the configuration at the benzylic carbon.…”

“…Subsequent transfer hydrogenation of the ion-pair intermediate 6 afforded the chiral isochromene 5. [16] The absolute configuration of the major enantiomer of 7 was determined to be R. [17] It was confirmed that the present reaction proceeded with inversion of the configuration at the benzylic carbon. [14,15] Further transformation of the chiral isochromenes was explored (Scheme 3).…”

From Waste Biomass to Solid Support: Lignosulfonate as a Cost‐Effective and Renewable Supporting Material for Catalysis

“…For safety and environmental reasons, we continued the reactions with ethanol. Further investigation revealed that the reaction was also affected by the other parameters including catalyst amount, temperature, and reaction time, and the optimal conditions should be 1.2 mol % of LS-Sc I, 808C, and 8 h (entries [16][17][18].…”

Novel Non‐toxic and Non‐hazardous Solvent Systems for the Chemistry of Indoles: Use of a Sulfone‐containing Brønsted Acid Ionic Liquid Catalyst in Butyl Acetate

“…In fact, several safer alternatives to classic dipolar aprotic solvents have been reported recently. We proposed the use of a NO 2 ‐functionalized imidazolium‐based ionic liquid as a solvent (or a solvent system component) to replace nitromethane, which is an explosive dipolar and aprotic solvent . Some interesting options have also been found in the field of bio‐based chemicals, such as cyrene ((−)‐dihydrolevoglucosenone), N ‐butylpyrrolidinone, γ‐valerolactone or 2‐methyltetrahydrofuran (2‐MeTHF) .…”