Charge‐Transfer Interactions: An Efficient Tool for Recycling Bis(oxazoline)‐Copper Complexes in Asymmetric Henry Reactions

Abstract

An anthracenyl-modified chiral bis(oxazoline) copper complex has been demonstrated to efficiently promote nitroaldol reactions between structurally varying aldehydes and nitromethane or nitroethane. The catalyst was recovered through formation of a charge transfer complex between the chiral ligand and trinitrofluorenone and its subsequent precipitation with pentane. The efficiency of this procedure was proved through several consecutive catalytic cycles that allowed the sturdy formation of the expected product with a high enantioselectivity. The catalyst's stability was also put to the test in an original multi-substrate procedure. Following the same recovery concept, a new heterogeneous procedure was tested for which trinitrofluorenone was covalently linked to a silica support. Asymmetric heterogeneous catalysis was performed under these conditions as one of the few examples demonstrating the potential catalyst recycling in nitroaldol reactions through reversible, non-covalent interactions.

Alkynyl Fischer Carbenes as a Platform for the Production of Difluorodiazaborinine Complexes via β‐Amino‐azadienes

“…Additionally, complexes of β‐amino‐1‐azadienes have generated a great deal of interest in the construction of tunable fluorescent probes analogous to the well‐known fluorophore BODIPY . Due to the versatility in terms of the catalysis, a number of different strategies have been used for their synthesis …”

Recent Applications of C 1-Symmetric Bis(oxazoline)-Containing Ligands in Asymmetric Catalysis

“…It was employed in asymmetric Henry reactions with enantiomeric excess values reaching up to 91% (Scheme 37). 61 A silica-supported TNF was also synthesized and the resulting ligand complex was also applied in the nitroaldol reaction of aldehydes of type 14 and nitromethane (108a) and nitroethane (108b).…”

Immobilization of an Anthracene‐Tagged Ruthenium Complex on a 2,4,7‐Trinitrofluoren‐9‐one‐Grafted Silica: Efficiency and Recyclability in Olefin Metathesis Reactions

“…In this context, new copper bis(oxazoline)‐type complexes modified by an anthracene functionality were demonstrated to catalyze asymmetric C–C bond formation (Henry, Ene, Diels–Alder reactions, etc.) in the presence of TNF‐tagged silica, and they were efficiently recovered and then reused by simple filtration of the noncovalently modified support 16. This recycling strategy is thus considered as a new tool for the easy immobilization of ruthenium complexes and their subsequent reuse in OM reactions.…”