50674-00-5Relevant academic research and scientific papers
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
Casimiro, Maria,Ona-Burgos, Pascual,Meyer, Jens,Styra, Steffen,Kuzu, Istemi,Breher, Frank,Fernandez, Ignacio
, p. 691 - 701 (2013)
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 benzyllithium× pmdta (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. To pair or not to pair: 2D 7Li,15N heteronuclear shift correlation has been applied to several lithiumorganyls consisting of polydentate N ligands such as N,N,N,N-tetramethylethylenediamine, N,N,N,N,N′- pentamethyldiethylentriamine and (-)-sparteine. In combination with other spectroscopic techniques, details on the formation of the lithiumorganyl- polyamine adducts the strength of ion pairing in solution have been explored (see figure). Copyright
