Impact of substituents on bromination sites of (E)-1-[5-methyl-1-aryl-1H-1,2,3-triazol-4-yl]-3-arylprop-2-en-1-ones using N-bromosuccinimide: Synthesis and crystal structure elucidation

Abstract

The bromination of (E)-1-[1-aryl-5-methyl-1H-1,2,3-triazol-4-yl]-3-arylprop-2-en-1-ones using N-bromosuccinimide (NBS) in polar protic solvents, such as methanol and ethanol, under acidic conditions was investigated. The bromination site was found to depend on the substituents in chalcones and the reaction conditions. Bromination of phenyl, 4-chlorophenyl, and 4-fluorophenyl-1H-1,2,3-triazolyl chalcones using NBS in methanol occurred at the aliphatic carbon-carbon double bond, producing the corresponding α‑methoxy bromide derivatives with a 90–95 % yield. In contrast, bromination of chalcones with a 4-methoxyphenyl group attached to the unsaturated center under similar conditions resulted in bromination on both the aliphatic double bond and ortho to the methoxy group on the aryl ring, producing the corresponding dibrominated triazoles in 85–90 % yields. When chalcones with a phenyl group on the triazole ring and a phenyl or 4-methoxyphenyl group on the unsaturated center were treated with NBS in ethanol, bromination occurred at the aliphatic double bond, yielding α-ethoxy bromide derivatives in 90–92 % yield. The crystal structures of the synthesized compounds have been determined to confirm their molecular structures, and Hirshfeld surfaces have been utilized to analyze intermolecular interactions within the crystals.