The sulfinamides 3 were transformed to sulfenimines 4 by treatment with thionyl chloride and a weak base such as quinoline (or triethylamine). The sulfenimines 4 were methoxylated with lithium methoxide to give 7α-methoxysulfenamides 5, which were directly acylated with an acyl chloride to furnish cephamycin derivatives 6. There was a major difference between the acylation of 7α-methoxysulfenamides 5 and that of the 7α-H derivatives 7. Reduction of the imines 4a with metal hydrides gave 7β-sulfenaminocephalosporins 12 together with a small amount of the 7α-isomers 13. The synthetic sequence 4a→12→14 provides a useful method for the isomerization of 7α-aminocephalosporins 17 to the corresponding 7β-isomers 18.
用亚
硫酰氯和弱碱(如
喹啉或
三乙胺)将亚磺酰胺 3 转化为亚磺
酰亚胺 4。亚磺
酰亚胺 4 与
甲醇锂发生甲氧基化反应,生成 7α-甲氧基亚磺酰胺 5,然后直接与酰基
氯发生酰基化反应,生成头霉素衍
生物 6。7α-Methoxysulfenamides 5 的酰化过程与 7α-H 衍
生物 7 的酰化过程有很大不同。用
金属
氢化物还原
亚胺 4a,可得到 7β-亚磺酰胺
头孢菌素 12 以及少量 7α 异构体 13。合成序列 4a→12→14 为 7α
氨基
头孢菌素 17 异构化为相应的 7β 异构体 18 提供了有用的方法。