Tricyclic benzothiazinium salts 3 are prepared by
[2++4] polar cycloaddition of thionium intermediates 2A,
generated from the corresponding α-chloro sulfides 2, and dienes
in the presence of silver perchlorate. Ring transformation of
benzothiazinium salts 3 with a reducing agent such as Mg,
NaBH4 and Zn–AcOH or with a base, furnishes
spiro-vinylcyclopropane derivatives 4 in moderate to high yields.
Electrolysis of 3a at -1.4 V vs. SCE in acetonitrile also
affords vinylcyclopropane 4a (60%). These results indicate that both
ionic and radical mechanisms may account for the vinylcyclopropane
formation, although it is unclear as to the nature of the radical
intermediate. The stereochemistry of 4a was determined by X-ray analysis
showing that sulfur and the vinyl group are cis-orientated.
Ten-membered lactam sulfides 6 are obtained as the major product of
SmI2 reduction of 3.
三环苯并
噻嗪盐 3 是由相应的 α-Cloro
硫化物 2 生成的
噻吩中间体 2A 与二烯在
高氯酸银存在下进行 [2++4] 极环化反应制备的。苯并
噻嗪盐 3 与还原剂(如 Mg、NaBH4 和 Zn-AcOH)或碱进行环转化,可得到中等至高产率的螺
乙烯基环丙烷衍
生物 4。 在
乙腈中以 -1.4 V 对 SCE 电解 3a 也可得到
乙烯基环丙烷 4a(60%)。这些结果表明,虽然还不清楚自由基中间体的性质,但离子和自由基机制都可能是
乙烯基环丙烷形成的原因。通过 X 射线分析确定了 4a 的立体
化学结构,显示
硫和
乙烯基是顺式取向的。
SmI2 还原 3 的主要产物是十元内酰胺
硫化物 6。