Anomeric effect in 2-alkoxytetrahydropyrans studied by carbon-13 and oxygen-17 NMR chemical shifts

Abstract

vco 1710; NMR 1.15 (s, 9 ), 1.3-2.4 (m, 8 ), 4.05 (br m, 1 H), 4.8 (br m, NH); 19F NMR 155.5 (not resolved m).4,5-Tetramethylene-2-oxazolidone ( 19): DR: yNH 3450 (sharp), 3250 (br), i/co 1750; NMR 1.3-2.2 (m, 8 H), 4 (t, J = 4,1 H), 6.45 (s, 1 H), 7.46 (s, 5 H).JV-(tert-Butoxycarbonyl)-l-ethyl-7-azabicyclo[4.1.0]heptane (20d): crude product, IR t>co 1710; NMR 0.8-1.9 (m exhibiting a sharp s at 1.4, 22 H), 2,3 (m, 1 H). A 1-g (4.4 mmol) sample of 20d was allowed to react with NR3-2.5HF. The crude solid isolated (970 mg) exhibited only one signal in the 19F NMR spectrum; its NMR spectrum was consistent with pure 21dT. The structure of 21dT was confirmed by its hydrolysis to the amine 21aT in Olah's reagent, followed by Schotten-Baumann benzoylation to 24bT.JV-(tert-Butoxycarbonyl)-2-fluoro-2-ethylcyclohexylamine (21dT): yield 90; mp 107-109 °C (CH3CN); IR -3440, vCo 1710; NMR 0.9 (2 overlapping t,J= 7), 1.4 (s) and 1.2-2,2 (m, total 22 H), 3,85 (br m, 1 H), 4,7 (br m, 1 H); mass spectrum, mje

Calculation of NMR Chemical Shifts and Spin−Spin Coupling Constants in the Monosaccharide Methyl-β-d-xylopyranoside Using a Density Functional Theory Approach

“…A similar trend is observed for the exocyclic oxygen (O1) where the difference between these two ranges of the dihedral angle was somewhat larger (∼30 ppm). A strong dependence of 17 O shieldings on the dihedral angle has been observed in 2-alkoxytetrahydropyrans and discussed in terms of anomeric, exo-anomeric, and γ-gauche effects . These effects are closely related to stereoelectronic contributions and changes in geometry within the O5−C1−O1−C Me segment.…”

A New Route to Carbohydrates Enriched with Oxygen Isotopes

“…Nevertheless, natural-abundance 17 O spectroscopic investigations of a number of 2-alkoxytetrahydropyrans , and monosaccharides − have been reported by employing elevated temperatures (75−100 °C) in solvents of low viscosity to reduce line widths. These results suggested to us that 17 O NMR was of potential use in investigating oligosaccharide conformation.…”

Stereocontrolled Preparation of Spirocyclic Ethers by Intramolecular Trapping of Oxonium Ions with Allylsilanes

“…In order to probe whether the 4- or 6-methyl group is more controlling of the stereochemistry, attention was next directed to the trans -4,6-dimethyl example 25 . The starting point for this phase of the undertaking was the previously described lactone 30 . Hydride reduction of 30 to diol 31 was followed by protection of the primary hydroxyl as the tert -butyldimethylsilyl derivative (Scheme ).…”