5a,6a-Oxidopregnane-3,20-dione

The influence of the conformational factors, which play a decisive role in directing oxide fission in the above cases is no longer operative in the case of 3-keto-5a,6a-epoxides and their 3-ethylene ketals. With these substrates the —I effect of the BFs-complexed 3-keto or 3-ketal grouping predominates leading to the fluorohydrins. Thus, treatment of both 5a,6a-oxidopregnane-3,20-dione (35) and its 3,20-bisethylene ketal with BFg-etherate in benzene-ether affords in 45% yield the 6jff-fluoro-5a-hydroxy-derivative (36) and its 3-ethylene ketal, respectively. which are converted into the 6a-fluoro-A -CH3... 

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