Abstract
The conformation of the title compounds was determined in solution by 1H-NMR spectroscopy and in solid state by single-crystal X-ray diffraction (XRD) complemented with density functional theory. The compounds were found to exist exclusively in solution and solid state as trans-2-aminochalcone epoxides with strong intramolecular hydrogen bonding interaction between the amino and carbonyl groups. These 2-aminochalcone epoxides experienced a solvent effect in DMSO-d6, which resulted in an anomalous chemical shift for the α-hydrogen signal, presumably due to complexation of solute molecules with DMSO. The solute–solvent interaction would probably fix the trans conformation of epoxyketone such that α-H is more accessible to both aryl rings, and in turn, experience their combined anisotropic effect. Intermolecular interactions in the crystal structures were confirmed and quantified using the Hirshfeld surface analysis. Moreover, the trans stereochemistry of the α-epoxyketones facilitated direct one-pot sequential sulfuric acid-mediated ring opening and aryl migration to afford the corresponding 3-arylquinolin-4(1H)-ones (azaisoflavones).
Highlights
Epoxides are versatile synthetic intermediates for a wide range of natural products and biologically active compounds [1,2,3]
By the resonance effect, strong electron withdrawing groups have been found to widen the C–O–C bond angle and to lengthen the C–C bond of the epoxide ring significantly to lead to ring-opening reactions via C–C bond breaking [5]
The Hirshfeld (HF) surface analyses were obtained with the support of Crystal Explorer software [26] in order to explain the intermolecular interactions between molecules in the crystal as Crystals 2019, 9, x FOR PEER REVIEW
Summary
Epoxides are versatile synthetic intermediates for a wide range of natural products and biologically active compounds [1,2,3] They react with a variety of nucleophilic reagents under neutral, acidic or basic conditions via SN 2 mechanism to afford 1,2-disubstituted products with trans orientation of the nucleophile and leaving oxygen atom. By the resonance effect, strong electron withdrawing groups (e.g., methyl ester, 4-nitrophenyl and cyano group) have been found to widen the C–O–C bond angle and to lengthen the C–C bond of the epoxide ring significantly to lead to ring-opening reactions via C–C bond breaking [5]. The 2-hydroxychalcones, for example, have been found to undergo epoxidation of the carbon–carbon double bond using hydrogen peroxide under
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
