BF3 center dot Et2O-catalyzed rearrangement of 7-epimeric 3 beta,7-diacetoxy-9 beta,11 beta-epoxy-5 alpha-lanostanes. Formation of novel 19(10 - 9 beta)abeo- and 19(10 - 9 beta), 30(14 - 8 alpha)bis-abeo-lanostane derivatives

摘要

The boron trifluoride etherate catalyzed reaction of 7-epimeric 3 beta,7-diacetoxy-9 beta,11 beta-epoxy-5 alpha-lanostanes 1 and 2 in acetic anhydride resulted in the formation of a series of skeletally rearranged products, mainly 19(10 -> 9 beta)abeo-lanostanes. 19(10 -> 9 beta),30(14-8 alpha)Bis-abeo-lanostane derivative 5 possessing a novel type of the triterpene skeleton was formed as the major product in the reaction of 7 alpha-epimer 2. The direction and extent of rearrangements of 9 beta,11 beta-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 H-1 and C-13 NMR. The structure of compound 5 was confirmed by single-crystal X-ray diffraction. (C) 2009 Elsevier Ltd. All rights reserved.