Dual mechanism of zinc-proline catalyzed aldol reactions in water.
نویسندگان
چکیده
The aldol reaction of acetone with aldehydes in aqueous medium under catalysis by zinc-proline (Zn(L-Pro)2) and secondary amines such as proline, (2S,4R)-4-hydroxyproline (Hyp) and (S)-(+)-1-(2-pyrrolidinomethyl)pyrrolidine (PMP) is shown to proceed by an enamine mechanism, as evidenced by reductive trapping of the iminium intermediate, while the aldol reaction of dihydroxyacetone (DHA) under catalysis by zinc-proline and by general bases such as N-methylmorpholine (NMM) is shown to occur under rate-limiting deprotonation of the alpha-carbon and formation of an enolate intermediate.
منابع مشابه
Clarification of the role of water in proline-mediated aldol reactions.
The report by List, Lerner, and Barbas1 in 2000 of an intermolecular direct aldol reaction catalyzed by proline became an unexpected watershed for the field of organocatalysis.2-4 Pihko and co-workers4b,c were the first to observe significantly higher yields with addition of water to intermolecular aldol reactions, even allowing employment of stoichiometric substrate ratios in some cases. This ...
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The enzyme 4-oxalocrotonate tautomerase (4-OT), which has a catalytic N-terminal proline residue (Pro1), can promiscuously catalyze various carbon-carbon bond-forming reactions, including aldol condensation of acetaldehyde with benzaldehyde to yield cinnamaldehyde, and Michael-type addition of acetaldehyde to a wide variety of nitroalkenes to yield valuable γ-nitroaldehydes. To gain insight int...
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ورودعنوان ژورنال:
- Chemical communications
دوره 14 شماره
صفحات -
تاریخ انتشار 2006