The exocyclic olefin 3 enters into stereoselective cyclopropanations with dihalocarbenes on the steroid β-face to afford the protected spirooctane analogues 4 and 5.These intermediates are transformed into novel, highly strained steroid derivatives, like 9, by utilizing an intramolecular cyclopropylidene insertion reaction en route to pentacyclic, C(1)-C(11)ethano-bridged steroids 13-20.
Kuenzer, H.,Bittler, D.,Rosenberg, D.,Sauer, G.,Wiechert, R.