An Unusual Stereoselective Decarboxylation: A Key Reaction to an Important Intermediate for Carbapenem Antibiotics.

The dramatic difference in reactivity of the two diastereomeric acid esters 4A and 4B during decarboxylation has been thoroughly investigated. The (R) isomer 4A underwent decarboxylation to provide a 94:6 mixture of SA and 5B at 80 C in 5-6 h. Under the same conditions the (S) isomer 4B did not undergo decarboxylation and with further heating to 120 C gave mainly the ring-opened decomposition product 6 along with unidentified decomposition products. A mechanistic rationale for this unusual reactivity profile is provided.