- PROCESS FOR PRODUCING OPTICALLY ACTIVE AZETIDINE-2-CARBOXYLIC ACIDS
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An optically active N-protected azetidine-2-carboxylic acid (5) can be produced by preparing an optically active 4-amino-2-halobutyric acid (3), ???by halogenating an optically active 3-hydroxy-2-pyrrolidinone (1) with inversion of configuration to prepare an optically active 3-halo-2-pyrrolidinone (2) followed by hydrolysis or, ???by halogenating an optically active 4-amino-2-hydroxybutyric acid ester (6) with inversion of configuration to prepare an optically active 4-amino-2-halobutyric acid ester (7) followed by hydrolysis or, ???by halogenating the compound (6) with inversion of configuration to prepare the compound (7), cyclizing the same to prepare the compound (2) followed by hydrolysis,???further cyclizing the compound (3) followed by treating the reaction product with an amino group-protecting agent.The optical purity of the thus-obtained compound (5) can be improved further by recrystallization.
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