6-heptadienoic acidsystems with hydrogen peroxide in the presence of a catalytic amount of diphenyl diselenide leads to 5-(3-hydroxypropenyl)dihydrofuran-2-one systems with defined relative configuration at the 4 and 7 positions (carboxylicacid numbering). A system having a six-membered ring as part of the s-trans-diene system was an intermediate in a strigol total synthesis; a second system lacking the