Title steroids of formula (I) : (where R1 and R2 are H or acyl), which have very strong topical anti-inflammatory activity with only slight systemic side-effects, are prepd. by simultaneous addn. of F and Cl to the 9(11)-double bond of a cpd. (II); (where R'1 is acyl) (pref. by reaction with HF and N-chloro-succinimide), opt. esterification of a free 17-hydroxy gp., hydrolysis of the 21-acyloxy gp., and re-esterification of the 21-hydroxy gp.
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