Reaction of 2-Methylene-1,3-dicarbonyl Compounds Containing a CF3-Group with 1,3-Dienes

The Knoevenagel condensation of 1-substituted 4,4,4-trifluorobutan-1,3-diones with paraformaldehyde in the presence of cyclic and linear 1,3-dienes leads to Diels–Alder cycloadducts via in situ formation of the appropriate 2-methylene-1,3-dicarbonyl compounds 2(a–c). In the reactions with linear 1,3-dienes, compounds 2(a–c) react as dienophiles. In the case of the reactions with cyclic 1,3-dienes both normal and inverse demand Diels–Alder reactions take place.