Enantiodivergent Synthesis of Pyrrolo[2,1-<i>a</i>]isoquinolines Based on Diastereoselective Parham Cyclization and α-Amidoalkylation Reactions
作者:Inés González-Temprano、Iñaki Osante、Esther Lete、Nuria Sotomayor
DOI:10.1021/jo049672o
日期:2004.5.1
C-10b-substituted pyrrolo[2,1-a]isoquinolines starting from an enantiomerically pure N-phenethylnorborn-5-en-endo-2,3-dicarboxyimide 3a, with a 2-exo-hydroxy-10-bornylsulfinyl group as a chiral auxiliary, has been developed. The key transformations are derived from diastereoselective intramolecular cyclization of aryllithiums and α-amidoalkylation reactions, with the ethylidene bridge of the norbornene moiety
C-10b取代的吡咯并[2,1- a ]异喹啉的对映异构体合成是从对映体纯的N -phenethylnorborn-5-en-内酯-2,3-二羧酰亚胺3a与2- exo -hydroxy-10-bornylulfinyl作为手性助剂的基团已经开发出来。关键转化来自芳基锂的非对映选择性分子内环化反应和α-酰胺基烷基化反应,降冰片烯部分的亚乙基桥决定了这两种反应的立体化学结果。因此,酰亚胺3a上的有机锂加成-分子内α-酰胺基烷基化序列可立体选择性地提供R构型在C-12b处发生,而相应的碘化酰亚胺3b上的串联Parham环化-分子间α-酰胺基烷基化反应在完全控制立体选择性的情况下发生,从而导致C-12b上的差向异构体。随后还原性除去手性助剂和逆Diels-Alder反应,可得到高产率和光学纯度(> 99%ee)的(10b S)-和(10b R)-吡咯并异喹啉1。