The initial step is oxidation of an alkyl tartrate with periodic acid to form a glyoxylate ester. The reaction mixture contains some water as a byproduct (also, the periodic acid is added as a dihydrate) and a significant amount of periodic and iodic acid, causing the formation of geminal diols and hemiacetal esters. According to H NMR, the mixture contains only ~2 % of the desired aldehyde, in a monomeric or trimeric form. This is increased to ~30 % by addition of P 2 O 5 and a 1 h heating to 50 °C ( 1 H NMR signal at ~9.4 ppm), but not further even upon extended heating or use of a higher temperature. We have used this mixture in subsequent reaction steps.