Abstract
The Diels-Alder cyclodimer of 6-vinyl-7-oxabicyclo[2.2. 1]hept-5-en-2-one ((1RS,2SR,3SR,4RS,7RS,11SR, 12RS)-11-vinyl-15,16-dioxapentacyclo[10.2.1.1(4,7).0(2,11).0(3.8)]hexade c-8-ene-6,13-dione: 20) was converted into the corresponding 8,9-endo-epoxide ((1RS,2SR,3RS,4RS,7RS,8RS,9SR,11SR,12RS)-11-vinyl-8,9-epoxy-15, 16-dioxapentacyclo[10.2.1.1(4,7).0(2,11).0(3.8)]hexadecane-6,1 3-dione: 23) by successive chemoselective bromine addition, epoxidation and zinc-induced debromination. Epoxide ring heterolysis of 23 was accompanied by pinacolic rearrangement giving a 5a-vinyl-perhydro-1H-benz[e]inden-3,7-dione-3a-carbaldehyde derivative ((1RS,3RS, 3aSR,5SR,5aRS,6SR,8RS, 8aSR,8bSR)-1,3,3a,4,5,8,8a,8b-octahydro-10,11-dioxo-3a-vinyl-6H-1,3:5a,8 -diethanobenzo[1,2-c,3,4-c']difuran-5,6-diyl dipivalate: 24). Photo-reductive ethereal ring opening of the 7-oxabicyclo[2.2.1]heptan-2-one moiety of 24, followed by ozonolysis of the vinyl group provided a trans,transoid,cis-perhydro-1H-benz[e]inden-3,7-dione bearing a free 9-hydroxy group, two masked hydroxy groups at C-1, C-4, a masked carbaldehyde group at C-3a and a free carbaldehyde group at C-5a ((1RS,3SR,3aRS,4SR,5aSR,9RS, 9aSR,9bSR)-5a-formyl- 1,4,5,5a,6,7,8,9,9a,9b-decahydro-9-hydroxy-7, 10-dioxo-3H-1,3-ethanonaphtho[1,2-c]furan-3,3-diyl dipivalate: 5).