If {HEAD ~ the conversion} of {TAIL ~ 6β} hydroxy 6α,17α dimethylpregn 4 ene 3,20 dione into Medrogestone is carded out with the Lewis acid, boron trifluoride etherate, rather than with the more conventional agents such as SOCl2 /pyridine, POCl3 /pyridine or MsCl/Et3 N/DMAP/CH2 Cl2, reaction temperatures below about 65° C. are feasible and isomerization to 6,17α dimethylpregna 6,8 diene 3,20 dione is largely avoided 
If { HEAD ~ the conversion } of { TAIL ~ 6β } hydroxy 6α,17α dimethylpregn 4 ene 3,20 dione into Medrogestone is carded out with the Lewis acid , boron trifluoride etherate , rather than with the more conventional agents such as SOCl2 /pyridine , POCl3 /pyridine or MsCl / Et3 N / DMAP / CH2 Cl2 , reaction temperatures below about 65 ° C. are feasible and isomerization to 6,17α dimethylpregna 6,8 diene 3,20 dione is largely avoided
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