Investigations Towards the Synthesis of the Cucurbitacins

Studies aimed at the partial synthesis of Cucurbitacins from lanosterol or steroidal derivatives are described in three sections. Firstly, further studies on the cleavage of 9a,11a-epoxyandrost 4-ene-3,17-dione by BF3 and other Lewis acids are described with full structural details on the products obtained. Secondly, a series of 9a,lla-epoxylanostane derivatives were synthesized and the epoxide cleavage reaction studied. No methyl migration was detected, rather 11-ketones or 7,9(11)-dienes were obtained in varying amounts. An attempt was made to rationalize the formation of these products based on an intramolecular proton abstraction mechanism. The third section of this thesis describes a successful attempt at C9 -> C10 methyl migration in 9a,11a-epoxy-4,4-dimethylandrost-5 ene-3,17-dione, where a developing allylic carbonium ion at C-9 apparently drives the methyl migration in one direction giving only one product.