α-Methylenation of Aldehydes

Significance

A fast and chemoselective route to α-substituted acroleins is reported. Aqueous formaldehyde and several unfunctionalized as well as functionalized aldehydes 1 were used in an organocatalytic synthesis to give the α-methyl­enated products 2 in good to excellent yields (75-99%). Either pyrrolidine/propionic acid or the dipeptid Pro-β-Ala was used as the catalyst. The reactions were carried out in isopropanol at 45 °C for 1-25 hours. Already existing stereochemistry is not touched by these conditions and several protecting groups remain in the product. Also polymerization or crossed-adol products could not be observed. Other amine salts and amino acids were tested too, but were less active.