In the present work I investigated the Diels–Alder reaction between substituted 2H-pyran-2-ones and maleic anhydride. The starting 2H-pyran-2-ones were synthesised by “one pot” synthesis, resulting in various substituted 3-benzoylamino-2H-pyran-2-ones. The latter when reacted with maleic anhydride under thermal conditions usually form one of the two possible products: a bicyclic double adduct (derivatized bicyclo[2.2.2] octene) or a thermodynamically more stable aromatic product (isobenzofuran derivative). By optimizing the reaction conditions, I tried to prepare and isolate both types of products. The reactivity of 2H-pyran-2-ones with electron donor substituents in the reaction with maleic anhydride has been shown to be greater than the reactivity of 2H-pyran-2-ones with electron-withdrawing substituents, resulting in the formation of bicyclic double adducts (with good yields) in the former case and aromatic isobenzofuran products in the latter. In contrast, 2H-pyran-2-ones with electron donor substituents preferentially form a bicyclic adduct, which in most cases is poorly converted to aromatic even after a long reaction time and higher reaction temperature.
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