Palladium catalysed formal 6-endo-trig approaches to pumiliotoxin alkaloids: interception of the elusive cyclopropyl intermediate
作者:Stephanie Feutren、Helena McAlonan、David Montgomery、Paul J. Stevenson
DOI:10.1039/a909774k
日期:——
Intramolecular Heck cyclisation of (E)-vinyl bromides leads to indolizidines, related to pumiliotoxin alkaloids, in which the stereochemistry of the trisubstituted double bond undergoes inversion. A cyclopropyl intermediate, which is believed to be responsible for the double bond inversion, has been intercepted by forcing an ‘early’ β-hydride elimination on this species. The relative stereochemistry
分子内颈 环化(E)-乙烯基溴化物导致吲哚并立定,与pumiliotoxin有关生物碱,其中三取代双键的立体化学发生反转。一种环丙基中间产物被认为是造成双键倒置的原因,已通过强制在该物质上“尽早”消除β-氢化物而被拦截。这个的相对立体化学环丙基中间体决定了最终β-氢化物消除的区域选择性。在这种情况下,立体化学允许所有三个β-氢化物消除,从而产生三个同分异构产物的混合物,其双键的位置不同。发现(Z)-乙烯基溴化物的反应性比(E)-乙烯基溴化物小,但在环化唯一的反应产物是得到所需的共轭二烯,同时转化了乙烯基溴的立体化学。这种方法将允许快速立体选择性地获得基于二烯的pumiliotoxin生物碱。