Diastereoselective Alkylation of 8‐Phenylmenthyl 2‐Methylacetoacetate. Preparation of Enantiomerically Pure 4,4‐Disubstituted 2‐Pyrazolin‐5‐ ones.

Abstract Aklylation of (1 R ,3 S ,4 S )-8-phenylmenthyl 2-methylacetoacetate with alkyl halides affords 2-alkyl halides affords 2-alkyl-2-methylacetoacetates in diastereomeric ratios 72:28 to 85:15. The major R (at C-α) diastereoisomers are converted into enantiopure 4,4-disubstituted 2-pyrazolin-5-ones with recovery of the chiral inductor.