Asymmetric Friedel–Crafts Alkylation of Indoles with Methyl (E)-2-Oxo-4-aryl-3-butenoates Catalyzed by Sc(OTf)3/pybox
作者:Giovanni Desimoni、Giuseppe Faita、Marco Toscanini、Massimo Boiocchi
DOI:10.1002/chem.200701908
日期:2008.4.18
The asymmetric Friedel-Crafts reaction between a series of substituted indoles 2 a-l and methyl (E)-2-oxo-4-aryl-3-butenoates 3 a-c has been efficiently catalyzed by the scandium(III) triflate complex of (4'S,5'S)-2,6-bis[4'-(triisopropylsilyl)oxymethyl-5'-phenyl-1',3'-oxazolin-2'-yl] pyridine (pybox; 1). Substituted 4-(indol-3-yl)-2-oxo-4-arylbutyric acid methyl esters 4 a-n were usually formed in
(4'S,5'S的三氟甲磺酸((III)配合物已有效地催化了一系列取代的吲哚2 al与甲基(E)-2-氧代-4-芳基-3-丁烯酸酯3 ac之间的不对称Friedel-Crafts反应)-2,6-双[4'-(三异丙基甲硅烷基)氧基甲基-5'-苯基-1',3'-恶唑啉-2'-基]吡啶(pybox; 1)。取代基的电子特性和位置无关,通常以优异的产率形成取代的4-(吲哚-3-基)-2-氧代-4-芳基丁酸甲酯4an,对映选择性高达99%ee。在吲哚环上,尽管排除了位置2。该加合物可以作为稳定的烯醇互变异构体获得,并且讨论了具有酮结构的平衡。X射线晶体结构确定为4 m表示4R绝对构型,因此,确认了乔根森(Jorgensen)对于4 i。的提议。立体感应的意义可以通过在3,pybox 1和已经提出用于Diels-Alder / hetero-Diels-Alder以及丙酮酸盐的Mukaiyama-al