A 'one pot' synthesis of 2-aryl-4H-1-benzopyran-4-ones under coupled microwave Phase Transfer Catalysis (PTC) and ultrasonic irradiation PTC

A 'one pot' synthesis of 2-aryl-4H-1-benzopyran-4-ones (3a-3f) is being reported. A mixture of o-hydroxyacetophenone, aroyl chloride, powdered n-tetrabutylammonium hydrogen sulphate (n-TBAHSO(4)) and potassium hydroxide (KOH) were either irradiated by microwaves or sonicated in an ultrasonic cleaning bath to afford flavones directly. On the contrary, conventional liquid-liquid Phase Transfer Catalysis (PTC) using benzene as organic phase and aqueous KOH as the second phase afforded first beta-diketones in accordance with Baker-Venkataraman synthesis which upon cyclization by p-toluenesulphonic acid (p-TSA) gave desired flavones in the next step. PTC coupled with microwaves or ultrasound show enhanced yields, the clean reaction conditions require less time, and have easier workup protocol. All synthesized compounds were characterized by their Proton Magnetic Resonance (PMR), IR, FAB Mass and elemental analyses.