Enantioselective quaternization of 4-substituted oxazol-5-(4H)-ones using recoverable Cinchona-derived dimeric ammonium salts as phase-transfer organocatalysts

Dimeric anthracenyldimethyl-derived Cinchona ammonium salts are used as chiral organocatalysts (5 mol %) for the enantioselective 4-alkylation of 4-substituted azlactones. The corresponding adducts bearing a new quaternary center were obtained with up to 80% ee when using a dimeric ammonium salt derived from cinchonidine, and are precursors of α,α-disubstituted α-amino acids. The catalysts can be recovered almost quantitatively by precipitation in ether and reused without loss of activity.

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(S)-4-Benzyl-2-(4-(trifluoromethyl)phenyl)oxazol-5(4H)-oneC17H12F3NO2[α]D25=-0.5 (c 1, MeOH)Source of chirality: l-PhenylalanineAbsolute configuration: (S)

(S)-4-Benzyl-2-(4-chlorophenyl)oxazol-5(4H)-oneC16H12ClNO2[α]D25=-4.7 (c 1, MeOH)Source of chirality: l-PhenylalanineAbsolute configuration: (S)