Glycidic esters are versatile intermediates in organic synthesis. These compounds are most conveniently prepared in Darzens reaction of α-halogenoacids esters with carbonyl compounds¹, carried out in the presence of a base.

Looking for new method of synthesis of (2R, 3S)-3-phenylisoserine hydrochloride - an important intermediate on the route to Paclitaxel - we turned our attention to the reaction of (2R, 3R)-3-phenylglycidic acid with ammonia, which should lead to (2R, 3S)-3-phenylisoserine 1.

In the presented work we studied the influence of the solvent and temperature on the stereoselectivity of Darzens reaction between t-butyl chloroacetate and benzaldehyde carried out under phase transfer catalysis (PTC) conditions (conc. aq. solution of NaOH as a base in the presence of a catalytic amount of quaternary ammonium salt).

Previously we tested many chiral quats derived from cinchona alkaloids. We selected N-2,4-dichlorobenzylcynchonine bromide and investigated the influence of parameters mentioned on the reaction course. We examined toluene, diisopropyl ether, methylene chloride and THF at temperatures -15, 1 and 8˚C.

Until now, the higher conversion of benzaldehyde (95%), Z/E ratio of isomers of 2 (2/1) and enantiomeric excess of (2R,3R) isomer (20%) were obtained in toluene at 1˚C after 8 h. Further investigations of this reaction are in progress.

1. M. S. Newman, B. J. Magerlin, Org. Reactions, 5, 413 (1949)

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