Allylation of an 11-oxo-steroid, the protected adrenosterone, was studied to examine more closely the steric hindrance of such a ketosteroid. While the beta face exhibits, as well known, a strong steric hindrance, the alpha side appears to be only relatively hindered. A high diastercoselectivity was observed in the addition of crotyl magnesium bromide. (C) 2003 Elsevier Inc. All rights reserved.