Efficient Synthesis and Resolution of Pyrrolizidines

In only two steps the commercially available maleimide 1 is converted into the key pyrrolizidine carboxylic acid unit (2) of the telomerase inhibitor UCS1025A. A kinetic resolution through an enantioselective oxa-Michael lactonization and trituration of the resulting scalemic mixture allow for a virtually quantitative separation of a racemate into the enantiomers.