A mild and convenient oxidation of H-phosphinic acids

A new mild and convenient method of oxidation of H-phosphinic to the corresponding phosphonic acids was developed. Conversion of H-phosphinic acids into trivalent trimethylsilyl esters using hexamethyldisilazane, followed by their oxidation with air and subsequent methanolysis allowed obtaining the final compounds in good to excellent yields. The methodology was proved to be particularly useful for N-benzyloxycarbonyl-alpha-aminophosphinic acids. The scope and limitations of the reaction were additionally tested using a variety of both free and protected amino- and hydroxyphosphinates as substrates.