Diels-Alder cycloaddition versus ring-opening esterification: A computational study of the mechanism of formation of oxa-norbonene lactones from the reaction of furfuryl alcohol and itaconic anhydride

•Furfuryl alcohol reacts with itaconic anhydride to form 5-membered lactone ring.•The formation of a 6-membered oxa-norbonene lactone ring is unfavored.•The 5-membered lactone products are more stable than the 6-membered products.•The preferred pathway involves initial [4 + 2] addition followed by lactonization.•Substituents have no effects on the reaction pathways.