Diels-Alder reactions carbon-nitrogen bond formation

The Diels—Alder reaction is a reversible reaction and the direction of cycloaddition is favored because two tt-bonds are replaced by two a-bonds. The cycloreversion also occurs more readily when the diene and/or dienophile are particularly stable molecules (i.e., formation of an aromatic ring, nitrogen, carbon dioxide, ethene, ethyne, nitriles, etc.) or when one of them can be easily removed or consumed in a subsequent reaction (Scheme 4.20). 

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