BF3·Et2O-catalyzed rearrangement of 7-epimeric 3β,7-diacetoxy-9β,11β-epoxy-5α-lanostanes. Formation of novel 19(10→9β)abeo- and 19(10→9β), 30(14→8α)bis-abeo-lanostane derivatives

The boron trifluoride etherate catalyzed reaction of 7-epimeric 3β,7-diacetoxy-9β,11β-epoxy-5α-lanostanes 1 and 2 in acetic anhydride resulted in the formation of a series of skeletally rearranged products, mainly 19(10→9β)abeo-lanostanes. 19(10→9β),30(14→8α)Bis-abeo-lanostane derivative 5 possessing a novel type of the triterpene skeleton was formed as the major product in the reaction of 7α-epimer 2. The direction and extent of rearrangements of 9β,11β-epoxides 1 and 2 depends on the configuration of the 7-acetoxy group. The structures of the new compounds were determined on the basis of spectroscopic methods, mainly 1H and 13C NMR. The structure of compound 5 was confirmed by single-crystal X-ray diffraction.