Stereoselective reactions. 29. Lithium-hydrogen interchange between achiral tridentate lithium amides and chiral bidentate amines. An approach to catalytic enantioselective deprotonation

Abstract

1H-NMR spectral studies have shown that lithium-hydrogen interchange between a chiral bidentate amine ( (R)- 3b ) and an achiral tridentate lithium amide ( 5a) occurs rapidly in THF, favoring the exclusive formation of a chiral bidentate lithium amide ( (R)- 2b ) at equilibrium. This finding was applied to catalytic asymmetric deprotonation of prochiral 4-substituted cyclohexanones ( 1) using 0.3 equivalent of (R)- 3b in the presence of 2.4 equivalents of 5a in THF in the presence of DABCO and HMPA.