3-Methylazetidin-2-one and its precursors: Optical resolution and absolute configurations

Abstract Enantiomers of 3-methylazetidin-2-one — (3 R )-(+)- and (3S)-(−)- 1 and of 3-amino-2-methylpropionic acid — (2 R )-(−)- and (2S)-(+)- 2 were obtained from corresponding diastereomers of methyl (αS)-N-α-methylbenzyl-3-amino-2-methylpropionate 3A,B which had been separated by recrystallization of their salts 4A,B with p-toluenesulfonic acid. The absolute configurations of azetidinones (+)- and (−)- 1 and their diastereomeric precursors, i.e. amino esters 3A,B , ( αS )- N - α -methylbenzyl-3-amino-2-methylpropionic acids 5A,B , and ( αS )- N - α -methylbenzyl-3-methylazetidin-2-ones 6A,B were established by conversion of (+)- 1 to amino acid (2R)-(−)- 2 and of amino acid (2S)-(+)- 2 to (−)- 1 .