N,3,4-Trisubstituted pyrrolidines by electron transfer-induced oxidative cyclizations of N-allylic β-amino ester enolates
作者:Ullrich Jahn、František Kafka、Radek Pohl、Peter G. Jones
DOI:10.1016/j.tet.2009.10.034
日期:2009.12
Oxidative radical cyclizations starting from easily accessible N-allylic β-alanine esters are reported. Deprotonation generates the corresponding enolates, which are transformed efficiently into α-ester radicals by single electron transfer mediated by ferrocenium hexafluorophosphate. The stereochemistry of the radical 5-exo cyclization can be switched by the configuration of the enolate precursor.
据报道,从容易获得的N-烯丙基β-丙氨酸酯开始的氧化自由基环化。去质子化产生相应的烯醇化物,其通过六氟磷酸铁铈介导的单电子转移而有效地转化成α-酯自由基。自由基5-外环化的立体化学可以通过烯醇化物前体的构型来切换。报道了使用N-(1-苯乙基)-取代的β-氨基酯的不对称氧化自由基环化的第一实例。四种可能的非对映异构体中只有两种是由具有高顺式选择性的(E)-烯酸酯形成的。从(Z)-烯酸酯,形成另外的非对映异构体,其可能仅在螯合控制下形成。