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)° 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.