Green Synthesis and DFT Studies of Novel Schiff Bases and [1,4]Diazepin‐1(5 H )‐one Derivatives From Cinnamomum cassia Essential Oil

ABSTRACT

A series of novel Schiff bases and [1,4]diazepin‐1(5 H )‐one derivatives were synthesized from the essential oil of Cinnamomum cassia , using cinnamaldehyde—the major oil constituent—as a renewable starting material. In situ condensation of cinnamaldehyde with various amine derivatives was performed in ethanol at ambient temperature, affording the target compounds ( 3a–b , 4a–c , and 5a–c ) within 8 h. The products precipitated directly from the reaction medium, enabling straightforward isolation and providing moderate to excellent yields (58%–92%) with high purities. The structures of all synthesized compounds were elucidated using IR spectroscopy, high‐resolution mass spectrometry (HRMS), and comprehensive 1D and 2D NMR analyses. Notably, [1,4]diazepin‐1(5 H )‐one derivatives 4a–c were obtained as mixtures of diastereoisomers, as evidenced by NMR spectroscopy. Density functional theory (DFT) calculations were performed to investigate the optimized molecular geometries, electronic structures, frontier molecular orbitals, molecular electrostatic potential surfaces, and key reactivity descriptors, providing insight into the physicochemical properties of the synthesized compounds.