mixtures of dibromoderivatives. These results are at variance with previous reports regarding 3-exomethylene sulfides and sulfoxides. The stereochemistry of the dibromoderivatives was unambiguously determined via X ray crystallography of 5a, following 1H-NMR correlations. The single dibromo derivatives as well as the isomeric mixtures, can be dehydrobrominated to afford 3-bromomethyl cephem derivatives (7
将3-亚甲基-7-
邻苯二甲酰基对苯二甲酸-4-羧
甲基丙烯酸酯3,相应的(R)-氧化物2和1,1-二氧化物1加成
溴,得到二
溴代衍
生物的立体异构体混合物。这些结果与先前关于3-环氧
丙烷硫化物和亚砜的报道有所不同。遵循1H-NMR相关性,通过5a的X射线晶体学确定了二
溴代衍
生物的立体
化学。可以将单个二
溴衍
生物及其异构体混合物脱氢
溴化,以非常好的收率得到3-
溴甲基头孢烯衍
生物(7、8、9)。