Acid-catalyzed rearrangement of some steroidal isoxazolidines

Acid-catalyzed reaction of the steroidal Delta(1)-unsaturated 3 beta,5 beta -epoxyimino compound 2 and Delta(3)-unsaturated 1 beta,5 beta-epoxyimino pr oducts 3 and 7, results in intramolecular rearrangement involving the N-CH3 group to give the corresponding perhydro-3,1-oxazine derivatives 9-11. Und er similar reaction conditions, the saturated analogues 4, 6 and 8 remain u nchanged. The difference in reactivity between the unsaturated and saturate d compounds is studied and elucidated by the semiempirical molecular orbita l MNDO-PMS method. (C) 1999 Elsevier Science Ltd. All rights reserved.