Get access

On the Solution Behaviour of Benzyllithium⋅(−)-Sparteine Adducts and Related Lithium Organyls – A Case Study on Applying 7Li,15N{1H} HMQC and Further NMR Methods, Including Some Investigation into Asymmetric Synthesis

Authors

  • María Casimiro,

    1. Laboratory of Organic Chemistry, University of Almería, Carretera de Sacramento s/n 04120 Almería (Spain)
    Search for more papers by this author
  • Dr. Pascual Oña-Burgos,

    1. Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Engesserstr. 15, 76131 Karlsruhe (Germany)
    Search for more papers by this author
  • Dr. Jens Meyer,

    1. Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Engesserstr. 15, 76131 Karlsruhe (Germany)
    Search for more papers by this author
  • Steffen Styra,

    1. Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Engesserstr. 15, 76131 Karlsruhe (Germany)
    Search for more papers by this author
  • Dr. Istemi Kuzu,

    1. Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Engesserstr. 15, 76131 Karlsruhe (Germany)
    2. Present address: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str., 35043 Marburg (Germany)
    Search for more papers by this author
  • Prof. Dr. Frank Breher,

    Corresponding author
    1. Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Engesserstr. 15, 76131 Karlsruhe (Germany)
    • Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Engesserstr. 15, 76131 Karlsruhe (Germany)
    Search for more papers by this author
  • Prof. Dr. Ignacio Fernández

    Corresponding author
    1. Laboratory of Organic Chemistry, University of Almería, Carretera de Sacramento s/n 04120 Almería (Spain)
    • Laboratory of Organic Chemistry, University of Almería, Carretera de Sacramento s/n 04120 Almería (Spain)
    Search for more papers by this author

Abstract

2D 7Li,15N heteronuclear shift correlation through scalar coupling has successfully been applied to several lithium organyls consisting of polydentate N ligands such as N,N,N′,N′-tetramethylethylenediamine (tmeda), N,N,N′,N′,N′′-pentamethyldiethylentriamine (pmdta) and (−)-sparteine. Structural insights on the conformation of benzyllithiumpmdta (5) in a toluene solution and the strength of ion pairing in combination with PGSE NMR measurements, 1H,1H-NOESY and 1H,7Li-HOESY experiments are presented. By studying in detail the formation of 5 in solution, a transient species has been observed for the first time and assigned to a pre-complex of nBuLi and pmdta. In addition, the solution behaviour of the complex formed between benzyllithium and (−)-sparteine (8) has been studied by PGSE and multinuclear NMR spectroscopy. The straightforward synthesis and first applications in asymmetric lithiations are also reported, which show that the new system benzyllithium(−)-sparteine (8) provide poorer enantioselective induction than the classical nBuLi(−)-sparteine (6). The results were supported by deprotonation experiments confirming that the formation of 8 relies on two relevant factors, namely temperature and lithiating reagent. The existence of 8 may thus interfere with the asymmetric induction when the system nBuLi (−)-sparteine is used in the enantioselective deprotonations of N-Boc-N-(p-methoxyphenyl)-benzylamine conducted in toluene.

Ancillary