Rapid Organocatalytic Aldehyde‐Aldehyde Condensation Reactions

We report the results of the systematic optimization of the α‐methylenation of aldehydes with aqueous formaldehyde. A simple combination of a secondary amine catalyst and a weak acid co‐catalyst has been identified, allowing access to α‐substituted acroleins in a matter of minutes. In the absence of formaldehyde, the catalytic system promoted the self‐condensation reaction of α,β‐unsaturated aldehydes. Both of these reactions exhibited linear relationships between co‐catalyst acidities and reaction rates. A second‐order dependence of catalyst concentration was observed, pointing to the involvement of two molecules of the ammonium catalyst in the rate‐determining step. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)