Dexamethasone → 9alpha-Fluoro-11beta-hydroxy-16alpha-methylandrosta-1,4-diene-3,17-dione

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A solution of 33 g (84.09 mmole) of 9-fluoro-16α-methyl-11β,17,21-trihydroxypregna-1,4-diene-3,20-dione in 50% acetic acid (3 liters) was stirred with 320 g of sodium bismuthate at room temperature for 20 hours. The resulting brown suspension was filtered through a bed of deactivated silica powder and washed with 300 ml of 50% acetic acid. The filtrate was concentrated in vacuo to 500 ml, diluted with 250 ml of 20% hydrochloric acid and extracted with chloroform. The chloroform solution was washed with 20% hydrochloric acid and water, dried over anhydrous Na2SO4 and evaporated in vacuo to give a solid. This was dissolved in chloroform and chromatographed on a 250 g-silica gel column, eluting successively with chloroform and 1:4 ethyl acetate-chloroform to give 22.8 g (81.6%) of tlc-homogeneous title compound, melting point 240°-242° with consistent spectral data.

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