Reaction of Benzeneselenenyl Halides with 3-Keto Steroids. A Novel Method for a-Bromination

Recent studies on the introduction of the 1,2-double bond in 5α-estrane-3,17-dione (1) using benzeneselenenyl chloride1 showed the formation of an unusual product which was identified as 2-chloro-5α-estr-l-ene-3,17-dione (5). It was proposed that compound 5 was formed by electrophilic attack of the chloro group in PhSeCl on 2- (phenylselenenyl)-5α-estrane-3,17-dione (2) to yield 2- chloro-2-(phenylselenenyl)-5α-estrane-3,17-dione (4) which undergoes 1,4-elimination following H202 oxidation as described by Sharpless et al.² It is interesting to note that the yield of 2-chloro-5α-estrenedione (5) is dependent on the amounts of PhSeCl used in the reaction mixture. Thus, as the molar ratio of PhSeCl increases the yield of compound 5 increases with a corresponding decrease in the formation of both 4-estrene-3,17-dione and 5α-estr-lene- 3,17-dione (Table I).