Effect of achiral and mixed chiral ligands on the asymmetric synthesis of γ-nitrophosphonates via Michael addition

Changes in the diastereo- and/or enantioselectivity were observed when the Li-cinchonine catalyzed conjugate addition of phosphonates to nitroalkenes was carried out in the presence of achiral/chiral additives. Although the conjugate addition in the absence of such additives proceeded in better yields and selectivities as reported previously, the dramatic change in selectivity in the presence of additives provides an opportunity to synthesize different stereoisomers of the product, gamma-nitrophosphonate, using primarily the same chiral source. (C) 2008 Elsevier Ltd. All rights reserved.