Two cyclization directions of 4-((2-(2-aryl-2-oxoethoxy)phenyl)imino)-2,6-di‑tert-butylcyclohexa-2,5‑dien-1-one: synthesis, spectroscopic characterization, crystallographic studies, and Hirshfeld surface analysis

Abstract

Investigation of O-phenacyl ethers of N-arylquinone imines intramolecular cyclization has demonstrated that it could proceed via two possible pathways: the C–C-bond formation or Csingle bondN bond formation, yielding 1,4-benzoxazines or 1,3-benzoxazoles. It has been established that the key factor determining the pathway of the cyclization reaction is the nature of the substituent in the phenyl ring of the benzoyl fragment of O-phenacyl ethers of N-arylquinone imine. The presence of an acceptor substituent leads to the formation of spirooxazine, whereas the absence of a substituent or the presence of a significant donor effect leads to the formation of oxazole product. The structures of the obtained compounds were studied by HRMS and NMR spectroscopy, including various two-dimensional NMR techniques. The structural features of four benzoxazine compounds, one benzoxazolone, and two by-products were studied in detail using single crystal X-ray diffraction analysis. Intermolecular interactions and cavities in crystals of spirocyclohexadienes of the 1,4-benzoxazines series were studied using the CrystalExplorer 21.5 software package.