Synthesis and absolute configuration of three isomeric spiro-bis(2-pyrrolidinones)

Syntheses are described for three isomeric spiro-bis-(2-pyrrolidinones): 2,7-diazaspiro[4,4]nonane-3,8-dione ( II ), 2,7-diazaspiro[4.4]nonane-1,8-dione ( IV ) and 1,7-diazaspiro[4,4]nonane-2,8-dione ( IV ). All the syntheses were carried out starting from 3-carboxy-5-oxo-3-pyrrolidineacetic acid ( VIII ) of known configuration, allowing the assignation of absolute configuration to compounds II, IV and VI synthesized through stereochemically unequivocal reaction steps.