reaction mixture was then poured into ice water and extracted with chloroform the extract was washed with dil sodium bicarbonate soln and water dried over sodium sulfate and concentrated in vacuo to give the crude product which was recrystallized from ethyl acetate hexane yield 25 mg m p 183 u00b0 185 u00b0 c b an analogous experiment of a by using acetyl bromide instead of isobutyryl bromide provided 23 mg of the pure product after the similar treatment to a solution of betamethasone 17 21 methyl orthobutyrate 300 mg dissolved in dmf 1 ml acetyl bromide 0 08 ml was added then the reaction mixture was treated by the similar procedure as described in example 126 a to give 24 mg m p 184 u00b0 185 u00b0 c of the pure product to a solution of 9 u03b1 chloro 16 u03b2 methyl 17 u03b1 21 1 39 methoxy 1 39 methyl methylenedioxy pregna 1 4 diene 11 u03b2 hydroxy 3 20 dione 30 mg dissolved in hexamethylphosphoramide dichloromethane 3 1 1 ml acetyl bromide 0 08 ml was added the reaction mixture was allowed to stand at room temperature for 50 min the reaction mixture was then treated by the similar procedure as described in example 126 a to give the crude product which was recrystallized from acetone hexane yield 23 mg m p 213 u00b0 216 u00b0 c dec a to a solution of dexamethasone 17 21 ethyl orthopropionate 30 mg dissolved in dmf 1ml acetyl bromide 0 08 ml was added the reaction mixture was allowed to stand at room temperature for 50 min the reaction mixture was then poured into ice.