[C:1]([C:4]1[O:5][CH:6]=[C:7]([OH:11])[C:8](=[O:10])[CH:9]=1)([OH:3])=O.[C:12]([O:15]C(=O)C)(=O)[CH3:13].S(=O)(=O)(O)O.C(Cl)(=O)C([Cl:27])=O>ClCCl.CN(C)C=O>[C:12]([O:11][C:7]1[C:8](=[O:10])[CH:9]=[C:4]([C:1]([Cl:27])=[O:3])[O:5][CH:6]=1)(=[O:15])[CH3:13]2-Carboxy-5-hydroxypyran-4-one (20 mmole) (Chem.Abs., 1948,42,567; J. Gen. Chem., 1946,16, 2025), acetic anhydride (10 ml) and concentrated sulphuric acid (0.5 ml) were heated to reflux temperature. On cooling to 0° C., the 5-acetoxy compound crystallised (recrystallised from ethanol); δ(DMSO-d6); 2.27(s,3H); 7.05(s,1H); 8.10(s,1H). This compound (5 mmole) was treated with oxalyl chloride (10 mmole) in dichloromethane (5 ml) containing dimethylformamide (15 μl). After 30 minutes the solvent was evaporated, the residue dissolved in toluene (evaporated several times to remove oxalyl chloride) and on final evaporation crystallised to give 5-acetoxypyran-4-one-2-carbonyl chloride which was used directly.
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