[4+2] Cycloaddition of α,β-unsaturated acid anhydrides to 2-furylpiperidin-4-ones: The short route to annulated 8,10a-epoxypyrido[2,1-a]isoindoles

A one‐step preparation procedure of 8,10a‐epoxypyrido[2,1‐a]isoindoles and their 7‐carboxylic derivatives is reported. The key synthetic step includes the intramolecular exo‐Diels–Alder reaction (IMDAF) of N‐furfurylacrylamide, produced in situ from 2‐furylpiperidin‐4‐ones and α,β‐unsaturated acid anhydrides. The synthesis of the title compounds can be performed under mild conditions with a high level of regio‐ and stereoselectivity. The same strategy has been successfully used for the synthesis of 9,11a‐epoxyimidazo[4′,5′:3,4]pyrido[2,1‐a]isoindole‐8‐carboxylic acid from maleic anhydride and the spinacine derivatives – 4‐(2‐furyl)‐4,5,6,7‐tetrahydro‐3H‐imidazo[4,5‐c]pyridines. J. Heterocyclic Chem., (2010).