Studies on the Terpenoids and related Alicyclic Compounds. VIII. Chemical Transformation of α-Santonin into Arsantin and Arsanin

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Chemical transformations of α-santonin (V) into arsantin (IIIa) and arsanin (IVa) isolated from Artemisia santolina by Sidyakin, et al. were described. α-Epoxyketone (IX) was prepared from α-tetrahydrosantonin (VI) via three steps. Reductive ring-opening of IX with zinc dust in methanol in the presence of a small amount of acetic acid afforded arsantin (IIIa). IIIa was not coincident with the reported natural atsantin, which was probably identical with a dimorph of arsanin (IVa). β-Epoxy compound (XVI) was prepared from 1-en-3β-ol (XIVa) by Sharpless' procedure. Reductive ring-opening of β-epoxyketone (XVIII) by a method similar to described for arsantin gave 1β-hydroxyketone (IVa). The mp, nuclear magnetic resonance and infrared spectra of IVa were identical with those of natural arsanin.