Structural and conformational study of two solvates of a fulgenic acid derivative

Abstract

The X-ray structures of two solvates of a fulgenic acid derivative (1), which is an essential intermediate in the synthesis of compounds with possible cancer-protecting properties, have been determined. The compound is closely related to those forming the class of fulgides, which are characterised by remarkable optical properties, that probably owe their existence to extensive electronic conjugation allowed by planarity of large parts of the molecules, a feature shared by 1. A conformational study has been undertaken to investigate the conditions for the existence, or absence, of such geometrical features and to understand if possible intramolecular hydrogen bonds may play a structure-determining role. Computed energy barriers for rotations around three C–C bonds have shed light on the nature of conformational rearrangements operative for the equilibration detected on the NMR time scale. Intramolecular hydrogen bonds do not favour the planar arrangement of large moieties and are not found to be competitive with intermolecular hydrogen bonds.