Asymmetric construction of quaternary carbon centers by sequential conjugate addition of lithium amide and in situ alkylation: utility in the synthesis of (-)-aspidospermidine.

Chiral diether ligand-controlled asymmetric conjugate addition of a lithium amide to cyclopentenecarboxylate and subsequent in situ alkylation gave a chiral cyclopentane derivative bearing a quaternary carbon with high enantio- and diastereoselectivity. The cyclopentane derivative was converted successfully to (-)-aspidospermidine.