Ultrasound-promoted synthesis of flavones by oxidation of 2’-hydroxychalcones and flavanones using I2/DMSO

Flavones constitute a large class of natural products with a broad range of biological activities. Among various methods, flavones have been synthesized by the oxidation of 2’-hydroxychalcones and flavanones. Most of these oxidative methods are of limited use since toxic reagents are used. Furthermore, these procedures require prolonged reaction times and high temperatures. The demand for cleaner and efficient methods led us to explore a new system to prepare flavones using I₂/DMSO and ultrasonic irradiation as a reaction promoter. Initially, we prepared a series of 2’-hydroxychalcones     (3a-c) and flavanones (4a-c)       by  the   condensation of 2’-hydroxyacetophenone (1) with aromatic aldehydes (2a-c). The obtained mixture was then subjected to the oxidation condition shown above to furnish the target flavones (5a-c) after sonication during 60 min. The products were purified using silica-gel column chromatography (hexane/AcOEt (9:1)) to give 86-98% of yields.