A highly efficient and environmentally benign synthesis of 6,8-dibromoflavones, 8-bromoflavones, 5,7-dibromoaurones and 7-bromoaurones |
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Authors: | Abu T. Khan Papori Goswami |
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Affiliation: | Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, India |
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Abstract: | Various ring substituted 6,8-dibromoflavones (3a-e) as well as 8-bromoflavones (3f-j) can be synthesized easily from the corresponding 2′-hydroxychalcones (1a-j) in good yields and in two steps under environmentally benign reaction conditions. This can be achieved by bromination with concomitant cyclization by using a combination of vanadium pentoxide, hydrogen peroxide and ammonium bromide in dichloromethane-water at 0-5 °C, followed by dehydrobromination of the brominated products 2a-j using 0.2 M ethanolic KOH solution at ice-bath temperature. On the other hand, various 5,7-dibromoaurones and 7-bromoaurone derivatives 6a-c can be obtained, exclusively, from the corresponding 2′-acetoxychalcones (4a-c) in good yields and in two steps by tuning the reaction conditions. |
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Keywords: | 2&prime -Acetoxychalcones 2&prime -Hydroxychalcones Bromination Vanadium pentoxide Hydrogen peroxide Ammonium bromide 8-Bromoflavones 6,8-Dibromoflavones 7-Bromoaurones 5,7-Dibromoaurones |
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