Proline–threonine dipeptide as an organocatalyst for the direct asymmetric aldol reaction

A new proline–threonine (H-Pro-Thr-OH) dipeptide has been demonstrated as an efficient organocatalyst for a direct asymmetric aldol reaction. It was found that this new peptide-based catalyst efficiently catalyzed the reaction between an aldehyde and acetone to provide β-hydroxy ketones in good yields with good enantioselectivities.

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(S)-Benzyl 2-((2R,3S)-1-(benzyloxy)-3-hydroxy-1-oxobutan-2-ylcarbamoyl)pyrrolidine-1-carboxylateC24H28N2O6[α]D25=-53 (c 1, CHCl3)Source of chirality: l-proline, l-threonineAbsolute configuration: (2R,3S)

(S)-Benzyl 2-((2R,3S)-1-(benzyloxy)-3-(tert-butyldimethylsilyloxy)-1-oxobutan-2-ylcarbamoyl)pyrrolidine-1-carboxylateC30H42N2O6Si[α]D25=-30.4 (c 1.0, CHCl3)Source of chirality: l-proline, l-threonineAbsolute configuration: (2R,3S)

(2R,3S)-3-(tert-Butyldimethylsilyloxy)-2-(S)-pyrrolidine-2-carboxamido)butanoic acidC15H30N2O4Si[α]D25=-21.1 (c 0.5, CHCl3)Source of chirality: l-proline, l-threonineAbsolute configuration: (2R,3S)

(R)-4-(2-Fluorophenyl)-4-hydroxybutan-2-oneC10H11FO2[α]D25=+65.9 (c 1, CHCl3)Source of chirality: aldol reactionAbsolute configuration: (R)