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Keywords:

  • 2-Oxazolines;
  • 2-Substituted-2-oxazolinium salts;
  • Hydrolysis;
  • Reaction mechanisms

Abstract

Chlorination of 2-hydroxyethylamides containing electron-donor substituents such as alkyl, phenyl or alkyl- or alkyloxy-substituted phenyl at 23 °C with SOCl2 proceeds via 2-substituted-2-oxazolinium hydrochlorides that can be transformed in situ into 2-substituted-2-oxazolines by neutralization with a weak base. The mechanism of neutral and base-assisted hydrolysis of 2-substituted-2-oxazolinium salts occurs by the nucleophilic attack at the C2 rather than the C5 position of the ring and yields the N-substituted-(2-hydroxyethyl)amide via the rearrangement of an amino ester intermediate. The elucidation of the mechanisms of these two reactions provides a one-pot, two-step method for the synthesis of the 2-substituted-2-oxazolines and clarifies the limitations of the functionalization of 2-substituted-2-oxazolinium salts by hydrolysis under neutral and basic conditions.