The rearrangement of 3β-acetoxy-9,11-epoxylanostanes by boron trifluoride–diethyl ether

Abstract

The rearrangement of 3β-acetoxy-9β,11β-epoxylanostan-7-one (1b) by boron trifluoride–diethyl ether leads to the ring B-enlarged products 3β-acetoxy-9a-homo-19-norlanosta-1(10),9(11)-dien-7-one (4) and the isomeric 9a(10),9(11)-diene, as well as to the previously described cucurbitane (2a) and the new cucurbitanes 3β-acetoxy-11β-hydroxy-19(10→9β)abeo-lanost-1(10)-en-7-one (5a) and its acetate (5b). Rearrangement of 3β-acetoxy-9α,11α-epoxylanostan-7-one (1a) by boron trifluoride–diethyl ether effects migration of the angular methyl group at C-13 to give 3β-acetoxy-18(13→12β)abeo-lanosta-8,13(17)-dien-7-one (6). The ¹³C n.m.r. spectra of these skeletally modified lanosterol derivatives are discussed, including the cucurbitanes having 10α and 10β stereochemistry.