Synthesis, characterization and crystal structure of 4′-ethynylflavanone and its chalcone precursor

Abstract

The synthesis of (E)-4-ethynyl-2′-hydroxychalcone (7) and the 4′-ethynylflavanone (8), it's spectroscopic and X-ray characterization are described for both compounds. Products were prepared by reacting 4-bromobenzaldehyde (1) under Sonogashira coupling reaction conditions, in order to obtain the key intermediary 4-ethynylbenzaldehyde (3). Then, this intermediary was reacted with 2′-hydroxyacetophenone (4) under Claisen-Shchmidt conditions to render a mixture of (E)-4-ethynyl-2′-hydroxychalcone (7) and 4′-ethynylflavanone (8). Compounds were separated by column chromatography, and spectroscopically characterized. Also, an alternative synthetic route to 4′-ethynylflavanone (8) was tested; the known 4′-bromoflavanone (6) was reacted under Sonogashira coupling conditions, in order to obtain the intermediary 4′-(trimethylsilylethynyl)-flavanone (9), which under deprotection afforded the desired 4′-ethynylflavanone (8). The Synthesis of (E)-4-bromo-2′-hydroxychalcone (5) and 4′-bromoflavanone (6), used as precursors, is also described. The X-ray structure of (E)-4-bromo-2′-hydroxychalcone (5) is presented as well.