EFFECT OF LITHIUM-SALTS ON ENANTIOSELECTIVE DEPROTONATION OF CYCLIC-KETONES

The influence of LiCl on deprotonation of 2-tert-butyl-2-methyl-1,3-di oxan-5-one 1 and tropinone 8 with chiral lithium amide bases is descri bed. In most cases the enantioselectivity was much higher in the prese nce of 1 (or more) equivalent(s) of LiCl. In an extreme case the oppos ite enantiomers were obtained in the presence and in the absence of Li Cl. The magnitude of LiCl effects and the optimal amount of LiCl varie d with the ketone - lithium amide system. A new deprotonation procedur e which utilizes the amine hydrochloride for generation of the chiral lithium amide is described. The effects of other lithium salts includi ng LiBr, LiI, LiClO4 were also briefly examined.