Three sterically hindered 6-amino-5-cyano-2-methyl-4-(1-naphthyl)-4H-pyran-3-carboxylate derivatives

In the title compounds, 2-methoxyethyl 6-amino-5-cyano-2-methyl-4-(1-naphthyl)-4H-pyran-3-carboxylate, C21H20N2O4, (II), isopropyl 6-amino-5-cyano-2-methyl-4-(1-naphthyl)-4H-pyran-3-carboxylate, C21H20N2O3, (III), and ethyl 6-amino-5-cyano-2-methyl-4-(1-naphthyl)-4H-pyran-3-carboxylate, C20H18N2O3, (IV), the heterocyclic pyran ring adopts a flattened boat conformation. In (II) and (III), the carbonyl group and a double bond of the heterocyclic ring are mutually anti, but in (IV) they are mutually syn. The ester O atoms in (II) and (III) and the carbonyl O atom in (IV) participate in intramolecular C-H...O contacts to form six-membered rings. The dihedral angles between the naphthalene substituent and the closest four atoms of the heterocyclic ring are 73.3 (1), 71.0 (1) and 74.3 (1) degrees for (II)-(IV), respectively. In all three structures, only one H atom of the NH2 group takes part in N-H...O [in (II) and (III)] or N-H...N [in (IV)] intermolecular hydrogen bonds, and chains [in (II) and (III)] or dimers [in (IV)] are formed. In (II), weak intermolecular C-H...O and C-H...N hydrogen bonds, and in (III) intermolecular C-H...O hydrogen bonds link the chains into ladders along the a axis.