Enantiomerically pure 5-substituted 2-oxo-cyclopentanecarboxylates by conjugate addition of cuprates to asymmetric shielded 2-oxo-cyclopentenecarboxylates

Asymmetric shielded 2-oxo-cyclopentenecarboxylates 6n and 6x were prepared by transesterification of 2-oxo-cyclopentanecarboxylate 2 with camphor derived concave alcohols 1n and 1x and by subsequent introduction of a double bond via phenylselenides. Diastereoselective conjugate addition of equimolar amounts of mixed cuprates at -78 °C and deprotection by ethanolysis gave enantiomerically pure 5-substituted 2-oxo-cyclopentanecarboxylates 13-18 and ent-13-18, valuable as chiral building blocks in natural product synthesis.