Azidolysis of alpha,ss-epoxycarboxylic acids. A water-promoted process efficiently catalyzed by indium trichloride at pH 4.0

The catalytic efficiency of InCl3, Yb(OTf)(3), and Sc(OTf)(3) in the azidol ysis of alpha,beta -epoxycarboxylic acids has been studied in water and in organic solvents, for comparison using NaN3 and Me3SiN3 as the source of th e azido group. In water, the catalytic effectiveness of these metal salts s trongly depends on the pH of the aqueous medium and on the type of Lewis ac id catalyst. In water their catalytic activity is mostly due to the corresp onding aqua ion species, the concentration of which becomes significant whe n the pH of the aqueous medium is below the corresponding pK(1,1) hydrolysi s constant. The process is more efficient in water than in organic solvents . At pH 4.0, InCl3 is a far better catalyst than Yb(OTf)(3) or Sc(OTf)(3) a nd allows the highly regio- and diasteroselective preparation of beta -azid o-alpha -hydroxycarboxylic acids, which can be isolated in pure form in ver y high yields.