Compound 5
apiose aminooxazoline
Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.
2-Aminooxazole (4; 840 mg, 5 mmol) was added to a stirred solution of dihydroxyacetone (2q; 450 mg, 5 mmol) in D2O (5 mL). The solution was adjusted to pD 7 with dilute DCl/NaOD and the reaction was stirred at room temperature. 1H NMR spectra were periodically acquired for 2 d. rac-Apiose aminooxazolines 5 (77%), as an equilibrating mixture of threo-5 (67%) and erythro-5 (33%), were observed as the sole products. The reaction was lyophilised to give a yellow powder, which was dissolved in hot EtOH. Evaporation yielded small needle-like crystals embedded within an oily residue. Single crystal X-ray diffraction revealed the crystal obtained from the oily residue to be rac-threo-5. A pure analytical sample was obtained by silica gel column chromatography (MeOH/EtOAc 1:4). Analysis by 1H NMR spectroscopy (300 and 600 MHz) of the isolated powder indicated it to be threo-5 (Supplementary Figure 13), which underwent isomerisation in D2O to give an equilibrating mixture of threo-5 and erythro-5 (threo-5/erythro-5 95:5 (0.5 h), 85:15 (2 d), 71:29 (6 d). rac-Apiose aminooxazolines 5 were observed to undergo facile interconversion between erythro-5 and threo-5 through rotational interconversion via a C3'-achiral open-chain iminium species.
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319901805
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