Studies on an Oxidative 1,4‐Addition to s ‐ trans ‐1,3‐Dienes, a Key Reaction in a Strigol Total Synthesis

Oxidation of 4,6‐heptadienoic acid systems 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 (carboxylic acid 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 six‐membered ring is the subject of the present publication. We accomplished a stereoselective synthesis of the diene system by (i) trapping a π‐allyl palladium complex with lithium diphenylphosphinite to give an allylic diphenylphosphane oxide and (ii) a subsequent Horner−Wittig reaction. The species that brings about the oxidative 1,4‐addition is benzeneperoxyseleninic acid. We also report observations that shed some light on the mechanism. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)