Formation of N,O-Acetals in the Production of X-ray Contrast Agents

Acetylation of 1 with acetic anhydride, an important step in the preparation of iohexol, gave the corresponding acetanilide and minor amounts of a few byproducts, whose structures have been elucidated. Among the byproducts were some 1,3-oxazolidines which survived when the reaction was quenched by adding methanol and water under strong acidic conditions.