Synthetic studies toward bioactive cyclic peroxides from the marine sponge Plakortis angulospiculatus

[reaction: see text] The total synthesis of two stereoisomers of a bioactive cyclic peroxide isolated from the marine sponge Plakortis angulospiculatus has been achieved in 18 steps with an overall yield of 2.8%. Diels-Alder addition of singlet oxygen to an acyclic triene carboxylic acid precursor was used to construct the 3,6-dihydro-1,2-dioxin ring. By comparing spectral data of the synthesized compounds and the natural material, we tentatively assign the absolute stereochemistry for the natural product as 3S,6R,8S,10R.