Yoshimasa Machida

A Useful Method for the Dealkylation of Dialkyl Phosphonates

Abstract The conversion of dialkyl phosphonates (1) to phosphonic acids (2) is usually accomplished by heating 1 in concentrated HC1 or HBr.1 This method, however, is subject to interference by other functional groups. In connection with our synthetic studies on biologically active organophosphorus compounds, we were faced with the problem of effecting the dealkylation of 1 containing labile functional groups under mild conditions. At the time when we were engaged in this study, the only available method for this purpose was to heat 1 in chlorotrimethylsilane2. This reaction, albeit mild, takes several days and the yields are not always satisfactory. We wish to report a very mild and extremely efficient method for the dealkylation of 1. Our strategy for effect-

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

Abstract 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