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  • Title: Organocatalytic chemo-, (E/Z)- and enantioselective formal alkenylation of indole-derived hydroxylactams using o-hydroxystyrenes as a source of alkenyl group.
    Author: Zhang HH, Wang YM, Xie YW, Zhu ZQ, Shi F, Tu SJ.
    Journal: J Org Chem; 2014 Aug 01; 79(15):7141-51. PubMed ID: 25003819.
    Abstract:
    The first organocatalytic asymmetric formal alkenylation of multicyclic alcohols using non-metal-based alkenes instead of alkenyl metals as a source of an alkenyl group has been established via chiral phosphoric acid catalyzed tandem reactions. This transformation directly assembles isoindolo-β-carboline-derived hydroxylactams with o-hydroxystyrenes via an asymmetric cascade vinylogous addition/hydrogen elimination reaction sequence, offering an easy access to functionalized chiral isoindolo-β-carbolines with one quaternary stereogenic center in high chemo-, (E/Z)-, and enantioselectivities (up to >95:5 cr, >95:5 E/Z, 97:3 er). This approach also represents the first catalytic asymmetric formal alkenylation of isoindolo-β-carboline-derived hydroxylactams, which provides a useful strategy for functionalization of isoindolo-β-carbolines and synthesis of chiral isoindolo-β-carboline derivatives. In addition, the investigation on the activating mode revealed that the hydroxyl group in o-hydroxystyrene was essentially important for generating a hydrogen-bond interaction with the catalyst. The dual activation mode of hydrogen bond and ion pair between the catalyst and the substrates cooperatively facilitated the desired formal alkenylation reaction in a chemo- and stereoselective way.
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