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 degreesC followed by cyclization of the brominated. products 2a-f on treating with 0.2 M ethanolic KOH solution at 0-5 degreesC, 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. (C) 2001 Elsevier Science Ltd. All rights reserved.