Internal redox amidation of α,β-unsaturated aldehydes in ionic liquids. The electrochemical route

Chiral Carbon Dots Derived from Serine with Well-Defined Structure and Enantioselective Catalytic Activity

Carbon dots (C-Dots), with unique properties from tunable photoluminescence to biocompatibility, show wide applications in biotechnology, optoelectronic device and catalysis. Chiral C-Dots are expected to have strongly chirality-dependent biological and catalytic properties. For chiral C-Dots, a clear structure and quantitative structure-property relationship need to be clarified. Here, chiral C-Dots were fabricated by electrooxidation polymerization from serine enantiomers. The oxidized serine has a reversed chiral configuration to serine, which leads to the chiral C-Dots possessing inverse handedness compared with their raw materials. Electron circular dichroism spectrum, together with other diverse characterization techniques and theoretical calculations, confirmed that these chiral C-Dots (2-7 nm) have a well-defined primary structure of polycyclic dipeptide and possess a spatial structure with a c-axis of hexagonal symmetry and two cyclic dipeptides as the spatial structural unit. These chiral C-Dots also show enantioselective catalytic activity on DOPA enantiomers oxidation.

Electrogenerated NHCs in Organic Synthesis: Ionic Liquids vs Organic Solvents Effects

In the last twenty years, N-heterocyclic carbenes (NHCs) have been extensively studied for their application as organocatalysts in stereoselective synthesis as well as ligands for transition metals-promoted synthetic methodologies. Derived mainly from azolium salts, NHCs have demonstrated exceptional versatility in their generation usually performed by deprotonation or reduction (chemical or electrochemical). In particular, the generation of NHC under electrochemical conditions, starting from azolium-based ionic liquids, has proven to be a successful green approach and demonstrated wide applicability in organic synthesis. In this Personal Account, the application of electrogenerated NHCs in organic synthesis will be discussed, with a particular attention to the different reactivity in ionic liquids compared to classical organic solvents.

Electrochemical synthesis and amidation of benzoin: benzamides from benzaldehydes

The benzoin condensation starting from benzaldehyde and the subsequent benzoin amidation to benzamide can be efficiently carried out under very mild conditions in an electrolysis cell. Among the advantages of using electrochemistry to generate our active reagents, the use of the easily dosed and non pollutant electron, instead of stoichiometric amounts of redox reagents or bases, usually renders the electrochemical methodology “greener” than classical organic reactions. Benzoin is obtained in good yield (85 %) carrying out the reaction in the room temperature ionic liquid BMIm-BF4. In this electrochemical reaction this liquid salt assumes the double role of solvent-supporting electrolyte system and precatalyst, yielding the corresponding N-heterocyclic carbene. The subsequent benzoin amidation is carried out by electrochemically generated superoxide anion, in the presence of an aliphatic primary or secondary amine. In this case the system superoxide/molecular oxygen acts as base and oxidant, yielding very good yields of benzamides (up to 89 %).

N-Heterocyclic Carbene-Mediated Microfluidic Oxidative Electrosynthesis of Amides from Aldehydes

A flow process for N-Heterocyclic Carbene (NHC)-mediated anodic oxidative amidation of aldehydes is described, employing an undivided microfluidic electrolysis cell to oxidize Breslow intermediates. After electrochemical oxidation, the reaction of the intermediate N-acylated thiazolium cation with primary amines is completed by passage through a heating cell to achieve high conversion in a single pass. The flow mixing regimen circumvented the issue of competing imine formation between the aldehyde and amine substrates, which otherwise prevented formation of the desired product. High yields (71-99%), productivities (up to 2.6 g h(-1)), and current efficiencies (65-91%) were realized for 19 amides.

Ionic liquids as an electrolyte for the electro synthesis of organic compounds

The use of ionic liquids (ILs) as a solvent and an electrolyte for electro organic synthesis has been reviewed.