Halbsesselkonformation und kristallstrukturen von 3,4,6-tri-O-acetyl-1,5-anhydro-2-desoxy-D-arabino-hex-1-enitol und 2,3,4,6-tetra-O-acetyl-1,5-anhydro-D-arabino-hex-1-enitol

Stereochemical investigations of the methyl α-D-threo- and ethyl α-D-erythro- anomers of 4,6-di-O-acetyl-2,3-dideoxyhex-2-enopyranoside by X-ray diffraction methods

“…Koji6-Prodi6 et al (1976) reported for the same geometry elements: 1.440 (3), 1.394 (3) A and 112.5 (2) °. Much more dissymmetrized endocyclic C-O bonds were found recently for a 3,4,6-tri-Oacetyl-D-1,2-dideoxypyranoside derivative (GLUCAL) (Krajewski, Urbaficzyk-Lipkowska, Gluzifiski, Bleidelis & Kemme, 1978Vangehr, Luger & Paulsen, 1979): the bond lengths C(5)-O(1) and STEREOCHEMICAL INVESTIGATIONS OF CIIHI60 6 AND Cl2HlsO6 O(1)-C(1) found were 1.433 (6) and 1..364 (6) A, respectively, but the O(1) angle value was very close to those reported above: 113.8 (4) °. Such dissymmetry in the case of the GLUCAL molecule may be explained partly by different hybridization of both bonded C atoms [C(5)=C(sp 3) and C(1)=C(sp2)].…”

Crystal structure of [(2R,3R,4S)-3,4-bis(acetyloxy)-5-iodo-3,4-dihydro-2H-pyran-2-yl]methyl acetate

“…The substituents at the C3 and C4 sites occupy equatorial positions while that at atom C5 is bisectional. The crystal structure of the unsubstituted parent compound has been reported three times and also adopts a distorted half-boat conformation (Vangehr et al, 1979;Krajewski et al, 1979;Voelter et al, 1981).…”

“…For the structure of the unsubstituted parent compound, determined three times, and having a distorted half-boat conformation, see: Vangehr et al (1979); Krajewski et al (1979); Voelter et al (1981 Symmetry codes: (i) x À 1; y; z; (ii) x À 1 2 ; Ày þ 3 2 ; Àz þ 1.…”

The conformation of t‐butyl 2‐methoxy‐5, 6‐dihydro‐2 H‐pyran‐6‐carboxylates and 6,6′‐ disubstituted 2‐methoxy‐5,6‐dihydro‐2H‐pyran derivatives on the basis of 1H and 13 C NMR spectra

“…Therefore, compound 6 , occurring in a single conformation, must possess the configuration with the OMe and C0,Me groups cis positioned. A cis arrangement of methyl and methoxy groups creates a serious steric interaction and, therefore, a conformational equilibrium is the only choice for compound 7 (Fig. 1).…”