Asymmetric syntheses of the 1-hydroxymethyl-2-hydroxy substituted pyrrolizidines (−)-macronecine, (−)-petasinecine, (−)-1- epi -macronecine, (+)-1- epi -petasinecine and (+)-2- epi -rosmarinecine
作者:Marta Brambilla、Stephen G. Davies、Ai M. Fletcher、Paul M. Roberts、James E. Thomson
DOI:10.1016/j.tet.2016.09.047
日期:2016.11
Following this route, (−)-macronecine, (−)-petasinecine, (−)-1-epi-macronecine and (+)-1-epi-petasinecine were synthesised in 21, 14, 10 and 19% overall yield, respectively, in six steps or fewer from commercially available starting materials. An analogous strategy employing enantiopure tert-butyl (R,E)-4-(triethylsilyloxy)hepta-2,6-dienoate facilitated the asymmetric synthesis of (+)-2-epi-rosmarinecine
所有四种可能的非对映异构体1-羟基甲基-2-羟基取代的吡咯嗪,(-)-macronecine,(-)-petasinecine,(-)-1- epi- macronecine和(+)-1- epi- petasinecine的不对称合成,被报道。将(S)-N-苄基-N-(α-甲基苄基)酰胺锂加成到叔丁基(E)-庚2,6-二烯酸酯,然后在各种条件下与丙烯醛进行醛醇缩合反应,制得四种可能的非对映异构体β-氨基酯,并安装了所需的立体异构中心。在每种情况下,通过还原酯部分然后依次进行两步方案(涉及臭氧分解和氢解/双重还原环化),可以快速接近吡咯嗪烷骨架。按照此路线,分别以21%,14%,10%和19%的总收率合成了(-)-macronecine,(-)-petasinecine,(-)-1- epi- macronecine和(+)-1- epi- petasinecine ,从市售的起始原料开始