Dual mechanism of zinc-proline catalyzed aldol reactions in water.

Chemical communications (Cambridge, England) (2006-04-01)
Jacob Kofoed, Tamis Darbre, Jean-Louis Reymond
ABSTRACT

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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
trans-4-Hydroxy-L-proline, ≥99%
Sigma-Aldrich
trans-4-Hydroxy-L-proline, BioReagent, suitable for cell culture, ≥98.5%
Supelco
trans-4-Hydroxy-L-proline, analytical standard

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