Supramolecular interactions in X-ray structures of oxalamides: Green synthesis and characterization

Abstract

Nowadays one of the biggest challenges of chemists all over the world is to design eco-friendly synthesis with a high atom economy and low E-factor. Solvent-free reactions are one of the best ways to avoid waste. Here we report a short series of solvent-free synthesis of five oxalamides which were carried out between oxalyl chloride and the corresponding primary amines (2-fluoroaniline (1), 2,6-diisopropylaniline (2), 2,6-dimethylaniline (3), (1R)-1-phenylethanamine (4), and cis-myrtanylamine (5) in ice bath; the release of HCl was neutralized by a saturated NaOH solution. All oxalamides 1-5 were afforded in good yields with high purity. NMR and single-crystal X-ray diffraction results revealed the characteristic intermolecular and intramolecular interactions of N,N'-oxalamides across the amide core. Notably, the X-ray structure of 1 reveals that amide hydrogen presents a trifurcated character due to the intra and intermolecular hydrogen interactions. Additionally, the crystal structure of lithium complex 7 shows CH/π stacking between the aromatic rings and tetrahydrofuran molecules.