Selective β-Hydroxyethylation at the N-1 Position of a Pyrazolone: Synthesis of Benzyl 1-(β-Hydroxyethyl)-5-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carboxylate

Selective 2-hydroxyethylation at the N-1 position of benzyl 5-methyl-3-oxo-2-phenyl-2,3-dihydro-1 H-pyrazole-4-carboxylate with epoxides was achieved using either AlMe 3 or Mg(ClO 4 ) 2 under mild conditions. The epoxide ring opening was both regioselective and stereospecific. Moderate to excellent yields were obtained from mono- and disubstituted epoxides with the exception of CIS-dimethyl-2-butene oxide that gave only a trace amount of the product.