An enantioselective route to the marine toxin (+)-acetoxycrenulide is described. The early stages of the synthesis feature the conversion of (R)-citronellol into a butenolide whose sole stereogenic center is provided by the terpenic alcohol. Three contiguous chiral carbon atoms are subsequently set in the requisite absolute configuration by conjugate addition of an enantiopure allylphosphonamide reagent. The resulting product is transformed during several steps into a primary selenoxide whose thermal activation in dimethylacetamide at 220 degrees C promotes sequential 1,2-elimination and Claisen rearrangement. The cyclooctenone core of the target is formed in this step. The final stages of the synthesis involve a series of fully stereoselective reactions including Simmons-Smith cyclopropanation and controlled Dibal-H reduction. The naturally occurring dextrorotatory enantiomer of acetoxycrenulide was ultimately acquired.