Ene-diamine versus imine-amine isomeric preferences

Area of Science:

• Organic Chemistry
• Computational Chemistry

Background:

• Aldimine coupling is a key reaction in organic synthesis.
• Understanding tautomeric preferences is crucial for predicting compound stability and reactivity.

Purpose of the Study:

• To synthesize and characterize compounds with 1,2-ene-diamine and alpha-imine-amine motifs.
• To investigate the factors influencing isomeric preferences in these systems using computational methods.

Main Methods:

• Cyanide-catalyzed aldimine coupling for synthesis.
• Single-crystal X-ray diffraction for solid-state structure determination.
• Density functional theory (DFT) calculations (B3LYP/6-311++G(d,p)) for energy and isomeric preference analysis.

Main Results:

• Successful synthesis of 1,2,N,N'-tetraphenyletheylene-1,2-diamine (13) and (+/-)-2,3-di-(2-hydroxyphenyl)-1,2-dihydroquinoxaline (17).
• DFT calculations indicated near-identical energies for core ene-diamine and imine-amine structures.
• Pi conjugation in compound 13 slightly favors the ene-diamine tautomer, while intramolecular hydrogen bonding in 17 strongly favors the imine-amine tautomer.
• Calculated structures accurately matched experimentally determined structures via X-ray diffraction.

Conclusions:

• Cyanide-catalyzed aldimine coupling is effective for generating diverse diamine and imine-amine structures.
• Tautomeric stability is significantly modulated by electronic effects (conjugation) and non-covalent interactions (hydrogen bonding).
• DFT calculations provide reliable predictions of molecular structure and isomeric preferences, complementing experimental data.