Thermal Ring Contraction Reactions of 9-Aryl-5H,7H-[1,2,5]thiadiazolo[3,4-h][2,3,4]benzothiadiazepine 6,6-Dioxides. Experimental and Computational Studies for Understanding the Course of the Transformations

详细信息    查看全文

• 作者：Ferenc Bertha ; Tamás Kégl ; József Fetter ; Balázs Molnár ; András Dancsó ; Gábor Németh ; Gyula Simig ; Balázs Volk
• 刊名：Journal of Organic Chemistry
• 出版年：2017
• 出版时间：February 17, 2017
• 年：2017
• 卷：82
• 期：4
• 页码：1895-1903
• 全文大小：583K
• ISSN：1520-6904

文摘

When refluxing with sodium hydrogen carbonate in acetonitrile, 7-chloro-5-(4-fluorophenyl)-1,3-dihydro-2,3,4-benzothiadiazepine 2,2-dioxide afforded, after loss of dinitrogen and subsequent ring contraction, the corresponding sulfone in 83% yield. Similar treatment of the related thiadiazolo-fused tricycles, i.e. 9-aryl-5H,7H-[1,2,5]thiadiazolo[3,4-h][2,3,4]benzothiadiazepine 6,6-dioxides, resulted in a substantially different product mixture: formation of sultines and benzocyclobutenes was observed, while only small amounts of the sulfones were formed, if any. Density functional theory calculations support the mechanism proposed for the transformations involving a zwitterionic intermediate formed by the tautomerization of the thiadiazepine ring followed by dinitrogen extrusion. When starting from 7-chloro-substituted 2,3,4-benzothiadiazepine 2,2-dioxide, the formation of sulfone via o-quinodimethane is the preferred pathway from the zwitterion. However, in the case of thiadiazolobenzothiadiazepine 6,6-dioxides it has been found that the ring closure of the zwitterion leading to the formation of sultines was kinetically preferred over the loss of sulfur dioxide leading to o-quinodimethane, which is the key intermediate to benzocyclobutene-type products. The calculations explain the differences observed between the product distributions of the chloro-substituted and the thiadiazolo-fused derivatives.