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-traps-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 pi-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. ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).