Dynamic kinetic resolution utilizing 2-oxoimidazolidine-4-carboxylate as a chiral auxiliary: Stereoselective alkylation of alpha-bromo amides with malonic ester enolates

Stereoselective carbon-carbon bond formation by dynamic kinetic resolution using tert-butyl (4S)-1-methyl-2-oxoimidazolidine-4-carboxylate (1) as a chiral auxiliary was developed. Reaction of a diastereomeric mixture of tert-butyl (4S)-3-[(2RS)-2-bromoacyl]-1-methyl-2-oxoimidazolidine-4-carboxylates (2) with a malonic ester enolate in HMPA predominantly afforded tert-butyl (4S)-3-[(2R)-2-alkyl-3,3-bis(alkoxycarbonyl)propionyl]-1-methyl-2-oximidazolidine-4-carboxylate [(S,R)-8] in good yields. The stereoselectivity of this reaction was in accordance with our working hypothesis based on the conformational analysis of 2 and elucidated the unique characteristics of 1 as a novel chiral auxiliary for dynamic kinetic resolution. The alkylated products (S,R)-8ej,k were easily converted to chiral cx-alkyl succinic acid derivatives and chiral beta-amino acid derivatives, both of which have been known as key building blocks for the syntheses of a variety of biologically active compounds.