β‑Aryl-α-nitro-α,β-enals as Heterodienes and Dienophiles

As demonstrated with the β-(2-furyl)-substituted analogue <b>1b</b>, β-aryl-α-nitro-α,β-enals (<b>1</b>) behave as heterodienes against enamines and enol ethers using their enal unit (e.g., <b>1b</b> → <b>12</b>). α-Nitro-α,β-enals can act as well as highly reactive dienophiles to render adducts endowed with nitrogenated quaternary centers (e.g., <b>1b</b> → <b>15a</b>). A hetero-Diels–Alder (HDA)/Diels–Alder (DA) sequence from <b>1b</b> also proved feasible on serial treatment with ethyl vinyl ether and Danishefsky’s diene (<b>1b</b> → <b>14</b>)