Nitrosonium ion generated in situ from the reaction of t-BuNO2 and BF3·Et2 is an effective oximinylating agent for enol ethers derived from steroidal spiroketals. The scope and limitations of this method has been studied. The difficult reduction of C23 ketone to C23 (R)-alcohol has now been selectively achieved via L-Selectride® reduction. Application to cephalostatin intermediates is discussed.Key words: oximinylation, nitrosonium ion, steroid spiroketal, cephalostatins.