A method of preparation of 4,10b-dimethoxy-2a-benzoyloxy-5b,20-epoxy-1,13a-dihydroxy-9-oxo-19-norcycloprop[g]class-11-ene from 4-acetoxy-2a-benzoyloxy-5b,20-epoxy-1, 13a-dihydroxy-9-oxo-7b-trifluoromethylsulphonyloxy-class-11-ene with a reaction of a molecular bone in the sulfan.
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