Novel secosteroids arising from acid catalysed rearranagement of fluocinonide acetonide in the presence of Tf2O and TMSOTf

Treatment of 6 alpha,9 alpha-difluoro-11 beta,21-dihydroxy-3,20-dioxo-16 al pha,17 alpha-isopropylidenedioxypregna- 1,4-diene-21-yl acetate (fluocinoni de acetonide) with trifluoromethanesulfonic anhydride in the presence of tr imethylsilyl trifluoromethanesulfonate as catalyst gave the ketone 3 and fu ran 4 arising from cleavage of the C9-C10 bond and aromatisation of the A r ing, and fluocinonide 5. The ketone 3 was shown to be an intermediate in th e formation of furan 4. (C) 1999 Elsevier Science Ltd. All rights reserved.