(-)-Bis[(S)-1-phenylethyl]amine

(-)-Bis[(S)-1-phenylethyl]amine is used as a chiral resolution reagent in organic synthesis.

Preparative Methods of (-)-(S,S)-α,α′-Dimethyldibenzylamine: minor improvements to the original catalytic hydrogenation procedure have been described (eq 1). This method provides (S,S)-(-)-(1) with an optical purity of only 70%. Enantiomerically pure (S,S)-(-)-(1) can be obtained by recrystallization of the hydrochloride salt of this enriched material from water or the benzoate salt from isopropanol. A chemical reduction procedure has also been described that yields optically active (S,S)-(1) with 74% enantiomeric excess (eq 2). A significant improvement to the former procedures is the diastereoselective hydrogenation of imines catalyzed by rhodium/chiral diphosphines, which yields (S,S)-(1) with an optical purity of 99.4% (eq 3).

(-)-(S,S)-α,α′-Dimethyldibenzylamine is a starting material for the formation of chiral amide reagents; useful in the stereospecific deprotonation of prochiral ketones, and as a chirality transfer agent in the reactions of prochiral enolates; stereoselective conjugate addition of organometallic reagents to unsaturated carbonyl systems.^[1]

(-)-(S,S)-α,α′-Dimethyldibenzylamine is no special precautions have been noted in the literature. The free base is a clear distillable liquid that should be stored under an inert atmosphere to prevent air oxidation. Long term storage may lead to some coloration of the material.

Purification of (-)-(S,S)-α,α′-Dimethyldibenzylamine: the free base can be distilled. The HCl salt can be recrystallized from water, which removes diastereomeric impurities. The benzoate salt can be recrystallized from isopropanol.

1. (a) Eleveld, M. B.; Hogeveen, H.; Schudde, E. P. JOC 1986, 51, 3635. (b) Yoshida, T.; Harada, K. BCJ 1972, 45, 3706.