Mechanistic studies on the formal aza-Diels–Alder reactions of N-aryl imines: evidence for the non-concertedness under Lewis-acid catalysed conditions

The reaction of a para-methoxyaniline, ethyl glyoxalate-derived imine with a series of dienes has resulted in products, which initially suggest the operation of different modes of aza-Diels-Alder reaction. However, a more likely explanation is that a common reaction mechanism is operating, involving a step-wise Lewis-acid catalysed process, which only appears to behave similarly to alternative concerted cycloaddition reactions.