a(E)-1-Methoxy-1,3-butadiene and 1,1-Dimethoxy-1,3-butadiene in (4 + 2) Cycloadditions. A Mechanistic Comparison
详细信息    查看全文
  • 作者:Reiner Sustmann ; Surajin Tappanchai ; and Heinz Bandmann
  • 刊名:Journal of the American Chemical Society
  • 出版年:1996
  • 出版时间:December 18, 1996
  • 年:1996
  • 卷:118
  • 期:50
  • 页码:12555 - 12561
  • 全文大小:317K
  • 年卷期:v.118,no.50(December 18, 1996)
  • ISSN:1520-5126
文摘
The reactions of (E)-1-methoxy-1,3-butadiene(1) and 1,1-dimethoxy-1,3-butadiene (2) with aseries ofdienophiles of increasing electrophilicity are described.Stereochemical studies reveal that the cycloadditions of1are concerted processes, even for the most electron-deficient olefinsdimethyl dicyanofumarate and dimethyldicyanomaleate. 1,1-Dimethoxy-1,3-butadiene reacts under ourconditions (dilute solutions and temperatures 60C) only with those dienophiles which can give zwitterions out of theantiperiplanar conformation of the diene.Zwitterionic intermediates can be trapped by methanol. In thecase of tetracyanoethene the kinetics of decay of anintermediate, interpreted as the zwitterion, can be followed by stoppedflow techniques: Ea = 14.8 ± 0.2kcalmol-1, log A = 11.9 ± 0.1,H = 10.8 ± 0.1 kcalmol-1, S =-6.2 ± 0.1 cal mol-1K-1, and G =11.40 ±0.03 kcal mol-1.

© 2004-2018 中国地质图书馆版权所有 京ICP备05064691号 京公网安备11010802017129号

地址:北京市海淀区学院路29号 邮编:100083

电话:办公室:(+86 10)66554848;文献借阅、咨询服务、科技查新:66554700