Methyl 2-benzamido-4-(3,4-dimethoxyphenyl)-5-methylbenzoate and N-{5-benzoyl-2-[(Z)-2-methoxyethenyl]-4-methylphenyl}benzamide

Methyl 2-benzamido-4-(3,4-dimethoxyphenyl)-5-methylbenzoate, C₂₄H₂₃NO₅, (Ia), and N-{5-benzoyl-2-[(Z)-2-methoxyethenyl]-4-methylphenyl}benzamide, C₂₄H₂₁NO₃, (IIa), were formed via a Diels–Alder reaction of appropriately substituted 2H-pyran-2-ones and methyl propiolate or (Z)-1-methoxybut-1-en-3-yne, respectively. Each of these cycloadditions might yield two different regioisomers, but just one was obtained in each case. In (Ia), an intramolecular N—H...O hydrogen bond closes a six-membered ring. A chain is formed due to aromatic π–π interactions, and a three-dimensional framework structure is formed by a combination of C—H...O and C—H...π(arene) hydrogen bonds. Compound (IIa) was formed not only regioselectively but also chemoselectively, with just the triple bond reacting and the double bond remaining unchanged. Compound (IIa) crystallizes as N—H...O hydrogen-bonded dimers stabilized by aromatic π–π interactions. Dimers of (IIa) are connected into a chain by weak C—H...π(arene) interactions.