Kristall- und molekülstruktur des mono- O-isopropylidenderivatives der dimeren 1,6-anhydro-β- D- arabino-hexopyranos-3-ulose

Abstract

Acetonation of dimeric 1,6-anhydro-β- D- arabino-hexopyranos-3-ulose yields, besides a monomeric di- O-isopropylidene compound, the dimer 2, which crystallizes in space group P2 12 12 1 with a  1.3680 (9), b  1.0686 (7), and c  1.0319 (7) nm, Z  4. The crystal and molecular structure of 2 have been determined by X-ray analysis with direct methods and was refined to a final R w of 5.55% for 2468 reflections. Compound 2 has not the same dimeric structure as the parent compound with a central 1,4-dioxane ring, but contains instead a central 1,3-dioxolane ring. The pyranose ring bearing the isopropylidene group adopts an almost ideal sofa conformation, with a nearly planar arrangement of C-1, C-2, C-3, C-4, and C-5. By analogy, it was concluded that the dimeric mono- O-isopropylidene derivative 7 of 1,6-anhydro-β- D- xylo-hexopyranos-3-ulose has the same asymmetric structure. The 360-MHz 1H-n.m.r. spectra of both compounds are in full agreement with the proposed structures.