The configuration and conformation of di-d-fructose anhydride I. The crystal and molecular structure of 3,4,3′,4′-tetra-O- acetyl-6,6′-di(triphenylmethyl)-di-d-fructose anhydride I

The crystal structure of 3,4,3′,4′-tetra-O-acetyl-6,6′-di(triphenylmethyl)-di-d-fructose anhydride I (1) has been determined by single-crystal X-ray diffraction. The crystals are monoclinic, space group P21 with a = 16.399(2), b = 9.091(2), c = 17.946(4) Å, β = 103.66(1)° V = 2600(2) Å3, and Z = 2. The structure was refined to R = 0.044 and Rw = 0.051 for 4403 observed reflections. The structure analysis of 1 showed that the previously assigned chemical structure of di-d-fructose anhydride I is undoubtedly α-d-fructofuranose β-d- fructofuranose 1,2′:2,1′-dianhydride. The conformations of the furanose rings are E5 with P = 59.8 and τm = 43.2° for d-fructose 1, and 2T3 with P = −34.39° and τm39.64 ° for d-fructose 2. The two furanose fragments are linked by a 1,4-dioxane ring in a spiro arrangement. The 1,4-dioxane ring has a chair conformation with Cremer-Pople puckering parameters Q = 0.527 Å, φ = 72.2° and θ = 14.2°.