Intramolecular Cyclization of β-Amino and β-Ammonio Radicals: A New Synthetic Route to the 1-Azabicyclo[3.2.1]octyl- and -[2.2.1]heptyl Systems
作者:Ernest W. Della、Paul A. Smith
DOI:10.1021/jo000790v
日期:2000.10.1
with tributyltin hydride generates 58 which is found to cyclize with high regioselectivity, affording a convenient high-yielding synthesis of the endo/exo isomers of 3-carbethoxy-1-methyl-1-azoniabicyclo[2.2.1]heptyl bromide 57. The isomeric bicyclo[2.2.1]heptyl ester 63 was not detected. These observations are in accordance with predictions based upon frontier molecular orbital considerations.
用氢化三丁基锡处理1-(2-苯基硒乙基)-1,2,5,6-四氢吡啶(15)仅得到还原产物,表明5-己烯基9不愿进行闭环。如果通过在C4处引入酯基或通过其季铵盐来修饰自由基的性质,则很容易发生环化。尽管基团52给出了未被还原产物污染的1-甲基-1-氮杂双环[3.2.1。]辛基溴化物(55)的优异产率,但是21的双环产物伴随着一些还原的物质。后者中不需要的烯烃的产生可以通过使用季铵酯1-(2-溴乙基)-4-碳乙氧基-1-甲基-1,2,5,6-四氢吡啶鎓溴化物(35)消除。暴露于氢化三丁基锡,得到1:1个内酯/外酯混合物,分别是4-乙氧基-1-甲基-1-氮杂双环[3.2.1]辛基溴化物(37)。这些结果证明了当酯官能团与5-己烯基系统的双键连接时,酯官能团具有强大的极性效应,该性质可在自由基58的情况下得到利用。前体的处理,1-(2 -溴溴乙基)-3-碳乙氧基-1-甲基-3-吡咯啉溴化物(60)