The agreement of the B3LYP/6-31g(d) results with experimental results confirmed this functional/basis set combination as the most adequate for modelling the progress of these aldol reactions; thus, this method was used in the discussion through this study.
(ii) Despite the fairly expanded scope of tested computational methods, including a recently introduced functional (M062X), the B3LYP/6-31g(d) accounting for the orbital relaxation upon immersion in solution (i.e., geometry optimization in liquid state performed with CPCM) is still recommended as the most accurate and additionally cost effective approach, to probe reactivity and selectivity in this specific type of aldol reactions.
(iv) For the studied range of aldehydes the diastereoselectivities and conversions of the aldol reactions can be computationally reproduced (the exo,syn isomers are typically the most stable forms and dominate in the solventless reaction) and even predicted (no product with p-methoxybenzaldehyde).
Barbas III, "Proline-catalyzed direct asymmetric aldol reactions," Journal of the American Chemical Society, vol.
Kaavi, "Effect of additives on the proline-catalyzed ketone-aldehyde aldol reactions," Tetrahedron, vol.
Tomczuk, "Spontaneous and diastereoselective aldol reactions of cyclic [beta]-amino ketones in the presence of water," Tetrahedron Letters, vol.
reported the application of the chiral ionic liquid 1 and its derivatives as an organocatalyst for aldol reaction
; however, the aldol products were obtained in moderate yields and selectivities (up to 80% ee) .
Keywords: Aldol reactions, Green chemistry, Homogeneous catalysis, Phase-transfer catalysis, Proline amides, Pyridinium salts.
Then, the aldol reactions of acetone with several aldehydes with or without the catalysts 6, 7 and 8 in water were investigated.
General Procedure for Aldol Reactions withCatalysts 11 and 12
ConclusionIn conclusion, proline amide derivatives and chiral pyridinium salts, which were prepared easily from cheap, commercially available materials, were very effective catalysts in the aldol reactions of acetone with aromatic aldehydes.
Some examples have been reported on the use of organocatalysts in water which is an important approach to the principles of green chemistry .The aldol reaction is one of the mostimportant carbon-carbon bond forming reactions in modern organic synthesis as a key step in natural product synthesis and for the rapid access to polyoxygenated compounds.
Duthaler spoke about the use of cyclopentadienyltitanium-TADDOLS to mediate enantioselective additions of organolithium species to carbonyls and to effect aldol reactions
as well as additions of allyl titanium species to carbonyls.
The topics include electrophilic aromatic substitution, organometallic reagents, acid halides and anhydrides, aldol reactions
, amines, and proton (1H) nuclear magnetic resonance.
Extending the coverage of its predecessor, Modern Aldo Reactions, this reference focuses on the latest developments and offers new tools for use of the aldol reaction
in the development of natural products and pharmaceuticals.