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Poly(Ethylene Glycol)‐Supported Proline: A Versatile Catalyst for the Enantioselective Aldol and Iminoaldol Reactions
Author(s) -
Benaglia Maurizio,
Cinquini Mauro,
Cozzi Franco,
Puglisi Alessandra,
Celentano Giuseppe
Publication year - 2002
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/1615-4169(200207)344:5<533::aid-adsc533>3.0.co;2-y
Subject(s) - chemistry , enantioselective synthesis , aldol condensation , aldol reaction , ethylene glycol , catalysis , organic chemistry , peg ratio , enantiomeric excess , solubility , proline , polymer chemistry , acetone , condensation reaction , combinatorial chemistry , amino acid , biochemistry , finance , economics
(2 S ,4 R )‐4‐Hydroxyproline has been anchored to the monomethyl ether of poly(ethylene glycol), M W 5000, by means of a succinate spacer to afford a soluble, polymer‐supported catalyst (PEG‐Pro) for enantioselective aldol and iminoaldol condensation reactions. This organic catalyst can be considered as a minimalistic version of a type I aldolase enzyme, with the polymer chain replacing the enzyme's peptide backbone, and the proline residue acting as the enzyme's active site. In the presence of PEG‐Pro (0.25–0.35 mol equiv.), acetone reacted with enolizable and non‐enolizable aldehydes and imines to afford β ‐ketols and β ‐aminoketones in good yield and high enantiomeric excess (ee), comparable to those obtained using non‐supported proline derivatives as the catalysts. Extension of the PEG‐Pro‐promoted condensation to hydroxyacetone as the aldol donor opened an access to synthetically relevant anti‐α,β ‐dihydroxyketones and syn‐α ‐hydroxy‐ β ‐aminoketones, that were obtained in moderate to good yields, and good to high diastereo‐ and enantioselectivity. Exploiting its solubility properties, the PEG‐Pro catalyst was easily recovered and recycled to promote all of the above‐mentioned reactions, that occurred in slowly diminishing yields but virtually unchanged ee's.