SUBSTITUENT EFFECTS ON THE REACTIVITY OF 2-MORPHOLINOBUTADIENES IN THE PRESENCE OF DIENOPHILES

2-Morpholinobutadienes (1) behave like typical enamines in their reactions with dimethyl acetylenedicarboxylate (2), β-nitrostyrene (3), diethyl 2-oxomalonate (4), and benzaldehyde (5). The nature of the resulting products is strongly dependent on the conformation which the 2-aminobutadienes (1) can adopt, as a function of the substituents. Only when the substituents can participate in the course of the reaction may the 2-morpholinobutadienes behave like a 4π-system in a concerted process.