3-Methylazetidin-2-one and Its Precursors: Optical Resolution and Absolute Configurations.

Abstract Enantiomers of 3-methylazetidin-2-one — (3R)-(+)- and (3S)-(−)- 1 and of 3-amino-2-methylpropionic acid — (2R)-(−)- 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-ones6A,B were established by conversion of (+)-1 to amino acid (2R)-(−)- 2 and of amino acid (2S)-(+)- 2 to (−)-1.