Projects per year
Abstract
The solution structures of [Li-6]-i-PrLi complexed to (-)-sparteine and the (+)-sparteine surrogate in Et2O-d(10) and THF-d(8) at -80 degrees C have been determined using Li-6 and C-13 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.
Original language | English |
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Pages (from-to) | 15445-15450 |
Number of pages | 6 |
Journal | Journal of the American Chemical Society |
Volume | 132 |
Issue number | 43 |
DOIs | |
Publication status | Published - 3 Nov 2010 |
Keywords
- ENANTIOSELECTIVE SYNTHESES
- (+)-SPARTEINE SURROGATE
- ORGANOLITHIUM COMPOUNDS
- CRYSTAL-STRUCTURES
- ALPHA-LITHIATION
- PHENYLLITHIUM
- BUTYLLITHIUM
- SUBSTITUTION
- PYRROLIDINE
- REACTIVITY
Projects
- 1 Finished
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Back to Basics: Investigating Structure,reactivity and catalysis of organlithium diamine complexes
O'Brien, P. A. (Principal investigator), Hilmersson, G. (Researcher) & Carbone, G. (Student)
1/10/07 → 31/03/11
Project: Research project (funded) › Research