An environmentally benign synthesis of aurones and flavones from 2′-acetoxychalcones using n-tetrabutylammonium tribromide

A wide variety of aurones (3a–f) can be prepared exclusively from 2′-acetoxychalcones (1a–f) in high yields in two steps, by bromination using n-tetrabutylammonium tribromide (TBATB) in the presence of CaCO3 in CH2Cl2–MeOH (5:2) at 0–5°C followed by cyclization of the brominated products 2a–f on treating with 0.2 M ethanolic KOH solution at 0–5°C, respectively. In contrast various flavone derivatives 6a–f can be obtained exclusively from compounds 1a–f in fairly good yields, by brominating with the same reagent in CH2Cl2, followed by dehydrobromination and finally cyclization on treating with 0.1 M NaOMe solution.