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

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