the oxabicyclo[3.2.1]octa-2,6-diene 17 b by a formal intramolecular hetero-Diels-Alder reaction was observed and 17 b could be isolated in up to 69 % yield. To explore the scope of this new photochemical reaction, the new ring-attached (E,Z,E)-hexatrienes 4 a, 5 a and 6 b were synthesized by twofold Heck reactions from 1,2-dibromocycloalkenes 1-3 (59-66 %). While irridiation of the cyclopentene-attached
在尝试对先前报道的1,6-双甲
氧基羰基或1,6-双三
甲基甲
硅烷基取代的环(E,Z,E)-
1,3,5-己三烯4b,4c和5b进行光
化学诱导的电环化时,在图5c中,获得原料和它们的非对映异构体的平衡混合物,相应的(E,Z,Z)-己
三烯4b,4c和5b,5c。通过随后以良好的产率(77-83%)对(E,Z,Z)-己
三烯4b和5b进行热6pi-电环化,形成了所需的反式-二取代的环-退火的环
己二烯9b和10b。在相同条件下处理双甲
硅烷基取代的己
三烯(E,Z,E)-5 c或(E,Z,Z)-5 c时,确实发生了6pi电环化,但初级产物立即在很大程度上异构化,形成
环己烷-退火的环
己二烯10c-12c与
脱氢产物13、14c的混合物。当将双甲
氧基羰基取代的己
三烯(E,Z,E)-5 b照射较长时间(4.5 h)时,
氧杂环[3.2.1] octa-2,6-diene 17b逐渐形成。观察到正式的分子内异狄尔斯-阿尔德反应,可以分离出17