1266333-43-0Relevant articles and documents
Asymmetric deprotonation using s -BuLi or i -PrLi and chiral diamines in THF: The diamine matters
Carbone, Giorgio,O'Brien, Peter,Hilmersson, Goeran
, p. 15445 - 15450 (2010)
The solution structures of [6Li]-i-PrLi complexed to (-)-sparteine and the (+)-sparteine surrogate in Et2O-d10 and THF-d8 at -80 °C have been determined using 6Li and 13C NMR spectroscopy. In Et2O, i-PrLi/(-)-sparteine is a solvent-complexed heterodimer, whereas i-PrLi/(+)-sparteine surrogate is a head-to-tail homodimer. In THF, there was no complexation of (-)-sparteine to i-PrLi until ≥3.0 equiv (-)-sparteine and with 6.0 equiv (-)-sparteine, a monomer was characterized. In contrast, the (+)-sparteine surrogate readily complexed to i-PrLi in THF, and with 1.0 equiv (+)-sparteine surrogate, complete formation of a monomer was observed. The NMR spectroscopic study suggested that it should be possible to carry out highly enantioselective asymmetric deprotonation reactions using i-PrLi or s-BuLi/(+)-sparteine surrogate in THF. Hence, three different asymmetric deprotonation reactions (lithiation-trapping of N-Boc pyrrolidine, an O-alkyl carbamate, and a phosphine borane) were investigated; it was shown that reactions with (-)-sparteine in THF proceeded with low enantioselectivity, whereas the corresponding reactions with the (+)-sparteine surrogate occurred with high enantioselectivity. These are the first examples of highly enantioselective asymmetric deprotonation reactions using organolithium/diamine complexes in THF.
