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[摘要]：2D Li-7,N-15 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, H-1,H-1-NOESY and H-1,Li-7-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 precomplex 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-(pmethoxyphenyl)- benzylamine conducted in toluene. |
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