Enantioselective Synthesis of β-Amino Acids. 2. Preparation of the like Stereoisomers of 2-Methyl- and 2-Benzyl-3-aminobutanoic Acid

Article abstract of DOI:10.1021/jo00034a037

An improved procedure for the preparation of (R)- and (S)-3-aminobutanoic acids (2a) through diastereomer separation of the corresponding (1'S)-N-phenethyl derivatives 1 is reported.From 2a, the four possible stereoisomeric perhydropyrimidin-4-ones 4 were prepared through the amide 2c and the Schiff base 3.In the cyclization of 3, the cis products 4 predominate ca. 95:5.These heterocycles can be alkylated (LDA, RX), as demonstrated by methylation and benzylation, with formation of a single diastereoisomer (5, 6).Hydrolysis (6 N aqueous HCl) of these 5,6-dialkylperhydropyrimidin-4-ones leads to the free amino acids 7-10.