Polymerization of l-proline functionalized styrene and its catalytic performance as a supported organocatalyst for direct enantioselective aldol reaction

As an alternative approach to the graft modification of polymers to fabricate polymer-supported chiral organocatalysts in a bottom-up fashion, l-prolinamide functionalized polymers were prepared by general solution homopolymerization or copolymerization of l-proline functionalized styrene monomer in the presence of 1,4-divinylbenzene as the crosslinking agent. The catalytic performance of the as-prepared heterogeneous catalysts towards the direct enantioselective aldol reaction of ketones with a series of aromatic aldehydes was explored. Our findings indicate that the as-prepared heterogeneous catalysts can afford relevant aldol addition products with good yields (up to 96%), high diastereoselectivities (up to 8:92 dr) and excellent enantiomeric excess (up to 96%); they also exhibit good recyclability, retaining high yield and rate as well as good selectivity after several cycles.

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(S)-N-(4-Vinylphenyl)pyrrolidine-2-carboxamideC13H16N2O[α]D25 = −81.2 (c 0.81, CHCl3)Source of chirality: (S)-ProlineAbsolute configuration: (S)

(((9H-Fluoren-9-yl)methoxy)carbonyl)-1-(S)-2-pyrrolidinecarboxylic acidC20H19NO4[α]D25 = −34.2 (c 1.01, DMF)Source of chirality: (S)-ProlineAbsolute configuration: (S)

(S)-2-[(R)-Hydroxy(4-nitrophenyl)methyl]cyclohexanoneC13H16NO4[α]D20 = +12.8 (c 1.85, CHCl3)Source of chirality: Asymmetric synthesisAbsolute configuration: (S), 2-(R)

(S)-2-[(R)-Hydroxy(3-nitrophenyl)methyl]cyclohexanoneC13H16NO4[α]D24 = +32.5 (c 1.35, CHCl3)Source of chirality: Asymmetric synthesisAbsolute configuration: (S), 2-(R)

(S)-2-[(R)-Hydroxy(2-nitrophenyl)methyl]cyclohexanoneC13H16NO4[α]D24 = +19.8 (c 1.60, CHCl3)Source of chirality: Asymmetric synthesisAbsolute configuration: (S), 2-(R)

(S)-2-[(R)-Hydroxy(4-cyanophenyl)methyl]cyclohexanoneC14H16NO2[α]D24 = +23.3 (c 1.55, CHCl3)Source of chirality: Asymmetric synthesisAbsolute configuration: (S), 2-(R)

(S)-2-[(R)-Hydroxy(4-fluorophenyl)methyl]cyclohexanoneC13H16FO2[α]D22 = +27.5 (c 0.35, CHCl3)Source of chirality: Asymmetric synthesisAbsolute configuration: (S), 2-(R)

(S)-2-[(R)-Hydroxy(4-nitrophenyl)methyl]cyclopentanoneC12H13NO4[α]D22 = −30.6 (c 0.56, CHCl3)Source of chirality: Asymmetric synthesisAbsolute configuration: (S), 2-(R)