Sulfone 15, derived from D-glutamic acid, and aldehyde 23, made by diastereoselective alkylation, were linked and elaborated into enamine sulfone 33. This underwent 5-exo radical cyclization to 34, which was desulfonylated to (-)-35, a compound that represents the spirobicyclic core of halichlorine. (C) 1999 Elsevier Science Ltd. All rights reserved.