Oxidation of 4-Oxo-4H-1-Benzopyran-3-Carboxaldehydes with N-Bromosuccinimide

4-Oxo-4-H-1-benzopyran-3-carboxylic acids and their derivatives (esters and amides), 2 , are known to possess interesting pharmacological activities. 1 As part of our synthetic studies of biologically active compounds, we needed to prepare a variety of 2 (carboxylic acids, esters, amides, etc.). An elegant method for the preparation of 4-oxo-4H-1-benzopyran-3-carboxaldehydes, 1 , was reported independently by Nohara et al. 2 and Harnish. 3 However, despite a rather extensive effort by Nohara et al. , the oxidation of 1 to 2 (Y=OH) has not been realized in good yield; thus the yields by Jones oxidation, the best reported method, ranged only from 9.5 to 39%. 4