title: Regioselectivity in sequential nucleophilic substitution of tetrabromonaphthalene diimides.
abstract: Nucleophilic substitution of tetrabromosubstituted naphthalene diimides (NDIs) with aniline was studied in detail to explore the regioselectivity as three different diamino-substituted regioisomeric products can be formed. We found that the regioselectivity of the nucleophilic disubstitution of 2,3,6,7-tetrabromonaphthalene diimide with aniline is dependent on reaction solvents and additives. In dichloromethane and chloroform without an additive the 2,7-diamino-3,6-dibromo-NDI isomer was formed regioselectively, while in DMF under similar reaction conditions the 2,3-diamino-6,7-dibromo isomer was observed as the major regioisomer. The third possible regioisomer 2,6-diamino-3,7-dibromo product was formed, if at all, in an insignificant amount. Tetrabutylammonium fluoride (TBAF) additive exerts a dramatic effect on the regioselectivity of this reaction, as in dichloromethane without TBAF the 2,7-diamino isomer was formed regioselectively, while without TBAF the 2,3-diamino isomer was formed exclusively. This remarkable effect of TBAF can be rationalized in terms of a deprotonation of the monoamino-tribromo-NDI generated in the first step of this sequential reaction as an intermediate by fluoride ions leading to an anionic species as indicated by UV-vis and NMR experiments whose electronic properties direct the regioselective attack of the second amine molecule. Our efforts led to the exclusively regioselective synthesis of 2,7-diamino-3,6-dibromo- and 2,3-diamino-6,7-dibromo-NDIs for the first time.
authors: Institut für Organische Chemie and Center for Nanosystems Chemistry, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors: Sabin-Lucian
authors: SL
authors: Suraru
authors: Frank
authors: F
authors: Würthner
mesh_terms: D006842:Hydrocarbons, Brominated / Q000138:chemical synthesis / Q000737:chemistry*; D007094:Imides / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D006842:Hydrocarbons, Brominated; D007094:Imides