Unusual reversal of regioselectivity in antibody-mediated aldol additions with unsymmetrical methyl ketones
摘要:
A catalytic regio- and enantioselective aldol reaction of various unsymmetrical methyl ketones with para-nitrobenzaldehyde has been developed using aldolase antibodies as the catalysts. It has been found that the sense and level of regioselectivity for the reactions catalysed by antibody 38C2 and 33F12 are highly dependent on the structure of both the donor and the acceptor but in contrast, antibodies 84G3 and 93F3 catalyse the exclusive formation of the linear regioisomer independent of the structure of the reactants examined. The level of enantiocontrol is very high for most reactions. Both linear aldol enantiomers could be accessed through aldol or retro-aldol reactions using the same antibody. Theoretical studies on regioisomeric alpha- and beta-heteroatom substituted enamines derived from unsymmetrical ketones suggest that most of the linear aldol products formed in the presence of antibodies 84G3 and 93F3 must be formed from intermediate enamines which are not the thermodynamically most favourable. (C) 2003 Elsevier Ltd. All rights reserved.
Recoverable silica-gel supported binam-prolinamides as organocatalysts for the enantioselective solvent-free intra- and intermolecular aldol reaction
作者:Abraham Bañón-Caballero、Gabriela Guillena、Carmen Nájera、Enrico Faggi、Rosa María Sebastián、Adelina Vallribera
DOI:10.1016/j.tet.2012.11.097
日期:2013.1
supported binam-derived prolinamides are efficient organocatalysts for the direct intramolecular and intermolecular aldol reaction under solvent-free conditions using conventional magnetic stirring. These organocatalysts in combination with benzoic acid showed similar results to those obtained under similar homogeneous reaction conditions using an organocatalyst of related structure. For the intermolecular process
catalytic system for the enantioselective direct aldolreaction between different ketones and aldehydes under solvent-free or aqueous conditions. The polystyrene-supported N-sulfonyl-(Ra)-binam-D-prolinamide catalyst in combination with benzoic acid showed similar results to those obtained with unsupported N-tosyl-binam-derived prolinamide under similar reaction conditions. The aldol products were obtained
<i>N</i>-Tosyl-(<i>S</i><sub>a</sub>)-binam-<scp>l</scp>-prolinamide as Highly Efficient Bifunctional Organocatalyst for the General Enantioselective Solvent-Free Aldol Reaction
N-Tosyl-(S a)-binam-l-prolinamide (5 mol%) and benzoic acid (1 mol%) were used as catalysts in the enantioselective direct aldol reaction between different ketones and aldehydes under solvent-free conditions in the presence or absence of water. Under these reaction conditions it was possible to reduce the amount of required ketone to two equivalents to give the corresponding aldol products with high yields, regio-, diastereo- and enantioselectivities. The aldol reaction between aldehydes or the intramolecular aldol reaction can be also performed with excellent results.
(S)-NOBIN-L-prolinamide was employed as organocatalyst in the direct aldol reactions of different ketones and aromatic aldehydes using dioxane as solvent and in the presence of water as additive. Acetone led to the aldol products in up to 93% ee, while cyclic ketones furnished the anti-aldols in moderate to high yield, excellent diastereoselectivity (up to > 99/< 1 anti/syn ratio) and high ee (up to 95%). (c) 2007 Elsevier Ltd. All rights reserved.
Unprecedented Regiocontrol Using An Aldolase I Antibody