A considerable stereoselectivity was found during the hydroxy → halogen exchange reaction of 16,16-bis(hydroxymethyl)-17-oxo- and -17-β-hydroxy-3-methoxyestra-1,3,5(10)-trienes depending on the starting materials and on the conditions of the reaction. The 17-oxo steroid 1 is transformed by acetic acid/hydrogen bromide solely into 16β-acetoxymethyl-16α-bromomethyl-3-methoxyestra-1,3,5(10)-trien-17-one (3a). In contrast, the 17β-hydroxy steroid 4 yields a mixture of the two 16-epimers 7a and 8a. The formation of these brominated steroids can be interpreted in terms of front-side neighboring group participation. The hydroxy → halogen exchange of 16,16-bis(hydroxymethyl)-17β-hydroxy compound 4 with carbon tetrachloride or carbon tetrabromide in the presence of triphenylphosphine proceeds stereoselectively, and only the 16β-halomethyl epimers 8a and 8b are formed. Constitutions of the new steroids were proved by IR, 1H and 13C NMR spectra. The C-16 configuration of the epimeric pairs was determined by NOE measurements.
在16,16-二羟甲基-17-酮和17-β-羟基-3-甲氧基
雌甾-1,3,5(10)-
三烯的羟基→卤素交换反应中,发现了相当显著的立体选择性,这取决于起始材料和反应条件。17-
酮类类
固醇1仅由
醋酸/
溴化氢转化为16β-乙酰氧基甲基-16α-
溴甲基-3-甲氧基
雌甾-1,3,5(10)-
三烯-17-酮(3a)。相反,17β-羟基类
固醇4则生成两种16-视异构体7a和8a的混合物。这些
溴化类
固醇的形成可以通过前侧邻近基团参与的方式来解释。在
三苯基膦存在下,使用
四氯化碳或
四溴化碳对16,16-二羟甲基-17β-羟基化合物4进行羟基→卤素交换反应是立体选择性的,仅形成16β-卤甲基视异构体8a和8b。新类
固醇的构造通过红外光谱、1H和13C NMR光谱得到了证明。异构体对的C-16构型通过NOE测定法确定。