title: Enantioselective cascade Michael addition/cyclization reactions of 3-nitro-2H-chromenes with 3-isothiocyanato oxindoles: efficient synthesis of functionalized polycyclic spirooxindoles.
abstract: An unprecedented Zn(OTf)2-catalyzed asymmetric Michael addition/cyclization cascade of 3-nitro-2H-chromenes with 3-isothiocyanato oxindoles has been disclosed. This transformation provides an efficient access to various synthetically important polycyclic spirooxindoles in a highly stereoselective manner under mild conditions (72–99% yields, up to >95:5 d.r. and >99% ee). The reaction leads to the formation of three consecutive stereocenters, including 1,3-nonadjacent tetrasubstituted carbon stereocenters, in a single operation. A bifunctional activation model of the chiral Zn(OTf)2/bis(oxazoline) complex was proposed based on control experiments, wherein the ZnII moiety serves as a Lewis acid and the N atom of the free NH group acts as a Lewis base by a hydrogen-bonding interaction.
authors.forename: Fen
authors.initials: F
authors.lastname: Tan
authors.forename: Liang-Qiu
authors.initials: LQ
authors.lastname: Lu
authors.forename: Qing-Qing
authors.initials: QQ
authors.lastname: Yang
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
authors.forename: Qiao
authors.initials: Q
authors.lastname: Bian
authors.forename: Jia-Rong
authors.initials: JR
authors.lastname: Chen
authors.forename: Wen-Jing
authors.initials: WJ
authors.lastname: Xiao
mesh_terms: D001578:Benzopyrans / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D000078183:Oxindoles; D011083:Polycyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013141:Spiro Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D001578:Benzopyrans; D007211:Indoles; D000078183:Oxindoles; D011083:Polycyclic Compounds; D013141:Spiro Compounds; C022960:2-oxindole