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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)

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Simple ortho-alkylated anilines have been shown to be excellent iminium catalysts for the epoxidation reaction of a-substituted acroleins. A range of different a-substituted acroleins give the epoxide products in good to excellent yields and good chemoselectivity.

The reversible reaction of primary or secondary amines with enolizable aldehydes or ketones affords nucleophilic intermediates, enamines. With chiral amines, catalytic enantioselective reactions via enamine intermediates become possible. In this review, structure-activity relationships and the scope as well as current limitations of enamine catalysis are discussed.