Abstract
(6R)-6-(4-Oxopentyl)-5,6-dihydro-2H-pyran-2-one, a naturally occurring alpha,beta-unsaturated delta-lactone, and its (6S)-enantiomer have been synthesized stereoselectively starting from pentane-1,5-diol. The synthesis involves Maruoka asymmetric allylation and ring-closing metathesis as the key steps.