A HIGHLY BETA-STEREOSELECTIVE CATALYTIC EPOXIDATION OF DELTA(5)-UNSATURATED STEROIDS WITH A NOVEL RUTHENIUM(II) COMPLEX UNDER AEROBIC CONDITIONS

Catalytic beta-stereoselective epoxidation of Delta(5)-unsaturated ste roid derivatives has been effected by a novel ruthenium(II) bioxazolin e complex under aerobic conditions. The reactions are regio- and stere oselective. The reaction conditions provide the corresponding 5 beta,6 beta-epoxides with high degree of stereoselectivity (88-96%) in very good yields, while oxidation of steroid derivatives with peracids lead s to 5 alpha,6 alpha-epoxides as the major products. The overall confo rmation of the steroid nucleus is nearly planar in the cholesteryl est er, while it is bent at the junction between the rings A and B in the 5 beta,6 beta-epoxide. This change from pseudo-trans- to cis-stereoche mistry of the A-B ring junction provides more room for the catalyst to approach from the beta-face of the steroidal skeleton.