Three novel isomeric pyranocoumarins from Calophyllum teysmannii: Calanone, isocalanone and teysmanone A

Abstract

The crystal and molecular structures of the three title compounds, calanone [6-benzoyl-5-hydroxy-2,2-dimethyl-10-phenyl-2H,8H-benzo[1,2-b:3,4-b′] dipyran-8-one, (I)], isocalanone [6-benzoyl-5-hydroxy-8,8-dimethyl-4-phenyl-2H,8H-benzo[1,2-b:3,4-b′] dipyran-2-one, (II)] and teysmanone A [10-benzoyl-5-hydroxy-8,8-dimethyl-4-phenyl-2H,8H-benzo[1,2-b:5,4-b′] coumarin, (III)], all having formula C27H20O5 but different isomeric structures, are reported. All of the compounds have the basic coumarin structure. Strong intramolecular hydrogen bonding is present between the carbonyl and hydroxyl groups in (I) and (II), but medium strong intermolecular hydrogen bonding is present in (III). The nature of the hydrogen bonding determines the planarity of the PhC=O groups. Structures (I) and (II) have a similar PhC=O conformation dictated by intramolecular O-H⋯O=C hydrogen bonding, in which the carbonyl groups are twisted away from the phenyl ring. The C(E-ortho)-C(E)-C=O torsion angle is 32.8(2)° in (I) and -40.8(2)° in (II). In the absence of intramolecular hydrogen bonding, the C=O group is nearly in plane with the benzene ring in (III) with a C(E-ortho)-C(E)-C=O torsion angle of -2.7 (3)°.