Solvent‐free synthesis of chiral Schiff‐base ligands based on ferrocene under microwave irradiation and application to enantioselective nitroaldol (Henry) reaction

Abstract

Chiral Schiff-bases 3a-f based on ferrocene were designed and synthesized using solvent-free methods by mixing ferrocene carbaldehyde 1 with amino alcohols and amines 2a-f under microwave irradiation and classical method for the enantioselective nitroaldol (Henry) reaction. The Schiff-bases were obtained in shorter reaction times and improved yield under microwave irradiation method over classical method. The highest enantioselectivity was observed in ligand 3e (95% ee) when CH(2)Cl(2) was used as solvent.

Simple and Efficient Green Methods Involving Microwaves and Mechanochemistry for Synthesis of a Schiff Ligand, 3, 3′-([1,1′-Biphenyl]-4,4′- Diylbis(azanylylidene))bis(indolin-2-One) With Antimicrobial Activity

“…The diameter of the inhibition zones was measured. The relative percentage inhibition is determined using the following equation [23]:…”

“…Electromagnetic microwaves are an unconventional alternative for activating chemical reactions, either in the presence of the solvent or in its absence. Recently, some Schiff bases have been prepared using microwaves in the presence of the organic solvent [16,21] or in the absence of the solvent [22,23]. Green chemistry or sustainable chemistry is the field which is oriented towards obtaining chemical products by ecological methods, which minimize the use and generation of materials dangerous for the environment.…”

“…Unconventional methods have also been used to obtain Schiff bases. Of these we can mention microwave irradiation of the chemical medium containing solvent [16,21] and solvent-free microwave irradiation [22,23], ultrasound irradiation [24], and mechanochemical reactions [25][26][27]. We synthesized a Schiff base, 3,3'-([1,1'-biphenyl]-4,4'-diylbis(azanylylidene))bis(indolin-2-one), starting from 1H-indole-2,3-dione and 1,1'-biphenyl-4,4'-diamine.…”

Copper Complex of Aminoisoborneol Schiff Base Cu2(SBAIB‐d)2: An Efficient Catalyst for Direct Catalytic Asymmetric Nitroaldol (Henry) Reaction

“…The Cu(I) complex of phosphine‐Schiff base ligand 8 also yielded the corresponding product with only 80% ee 12b. Other Schiff bases 9 ,12d 11 ,12e and 12 12g were found to be inefficient ligands for the Henry reaction. Although the recently reported chiral Cu(II) complex of paracyclopane Schiff base 10 has shown good ee ,12f its substrate scope was limited only to 2‐nitrobenzaldehye.…”