title: Stereochemical surprises in the Lewis acid-mediated allylation of isatins.
abstract: The BF(3)·OEt(2)-mediated allylation of isatin with an α-chiral allylic stannane is diastereo- and enantioselective. Conversely, allylation of any substituted isatin employing the identical protocol is not diastereoselective at all and only enantioselective for the major diastereomer having syn relative configuration. The anti isomer is, however, formed in almost racemic form. Both absolute and relative configurations are unambiguously secured by X-ray analysis of major isomers, and the stereochemical assignment of the other 3-substituted 3-hydroxy oxindoles is based on similar NMR spectroscopic characteristics. The remarkable observations are rationalized by an acyclic transition state model.
authors.affiliation: Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany.
authors.forename: Devendra J
authors.initials: DJ
authors.lastname: Vyas
authors.forename: Roland
authors.initials: R
authors.lastname: Fröhlich
authors.forename: Martin
authors.initials: M
authors.lastname: Oestreich
mesh_terms: D000478:Alkylation; D001880:Boranes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007510:Isatin / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D013237:Stereoisomerism; D017971:Tin Compounds / Q000737:chemistry
chemical_list: D001880:Boranes; D017971:Tin Compounds; C031525:stannane; C101707:boron trifluoride etherate; D007510:Isatin