The title compd. (I), useful as intermediate for the manuf. of betametasone, was prepd. Partial ketalization of the trioxo compd. (II), KBH4 redn. of the resulting oxo compd. (III), and subsequent dehydration by MeSO2Cl contg. SO3 gave the epoxypregnene (IV). Grignard reaction of IV with MeMgBr gave the methylhydroxy deriv. (V) and subsequent deketalization the dione (VI), which on 2-step bromination-dehydrobromination or 1-step dehydrogenation by dichlorodicyanobenzoquinone led to I.