Homochiral complexed benzaldehydes 1-3 are converted in to optically pure imines 4-6 in good yields by reaction with benzylamine in ethanol-ether solution at room temperature.
Reaction conditions: i) EtOH/Et2O , room temperature.
The cycloaddition reaction of 4 with carbethoxymethansulfonyl chloride in the presence of Py as base and in THF at -78°C affords a diastereoisomeric mixture in 78:22 ratio of trans 3,4 disubstituted beta-sultams.
Reaction conditions: CH2Cl2 , Et3N , 0°C
The chromatographic separation of the two complexed diastereoisomers affords, after decomplexation, the enantiomerically pure beta-sultams 7 and 8 .
When the reaction was carried out starting from ortho substituted 2-CH3 and 2-Cl imines, the beta- sultams were obtained in low yields (45% and 24%) respectively.