Enantiomerically enriched preparation of enolizable beta-keto amides. Diastereoselective alpha-acylation and subsequent aminolysis of 2-acyl-3-phenyl-l-menthopyrazoles

After deprotonation with LDA, 2-acyl-3-phenyl-l-menthopyrazoles (13) were diastereomerically alpha-acylated to give N-(3-phenyl-l-menthopyrazolyl) beta-keto amides (14-19). The subsequent amides were converted into the corresponding N-alkyl amides (21-24) retaining their enantiomeric enrichment on the alpha-position. These are the first examples of enolizable beta-keto acid derivatives having only one chiral center at alpha-position. These chiral beta-keto amides were surprisingly stable in dry benzene and their optical asymmetries were almost retained for two weeks at room temperature without any epimerization. Copyright (C) 1996 Elsevier Science Ltd