1,2-Dehydrogenation of steroidal 6-methylen derivatives. Synthesis of exemestane

The development of an efficient dehydration method of steroidal 4-en-3-ones by using chloranil and BSTFA in the presence of triflic acid in refluxing toluene allowed us, starting from testosterone, to set a large-scale procedure for the synthesis of the anti-cancer drug exemestane in 70% overall yield.