Journal of the American Chemical Society, Vol.126, No.47, 15473-15479, 2004
Is the A-ring of sparteine essential for high enantioselectivity in the asymmetric lithiation-substitution of N-Boc-pyrrolidine?
The simplest chiral portion of sparteine, N,N'-dimethyl-2-endo-methylbispidine, was prepared and evaluated in the asymmetric lithiation-substitution of N-Boc-pyrrolidine. The results indicate that the complete A-ring of sparteine is essential for high levels of asymmetric induction. DFT-QSSR analyses of the diamine/Li+ complexes and DFT calculations of the pertinent i-PrLi/diamine/N-Boc-pyrrolidine complexes are predictive and provide complementary pictures of the stereochemical features critical to this transformation.