C1(C)C=CC(S([N:10]2[CH2:16][C:12]3([CH2:15][O:14][CH2:13]3)[CH2:11]2)(=O)=O)=CC=1.[Mg].O.O.O.O.O.O.O.O.O.O.S([O-])([O-])(=O)=O.[Na+].[Na+].S([O-])([O-])(=O)=O.[Na+].[Na+].[C:43]([OH:48])(=[O:47])[C:44]([OH:46])=[O:45]>CO.C(O)C.C(OCC)C>[C:43]([OH:48])(=[O:47])[C:44]([OH:46])=[O:45].[CH2:13]1[C:12]2([CH2:16][NH:10][CH2:11]2)[CH2:15][O:14]1.[CH2:13]1[C:12]2([CH2:16][NH:10][CH2:11]2)[CH2:15][O:14]16-(Toluene-4-sulfonyl)-2-oxa-6-azaspiro[3.3]heptane (510 mg, 2 mmol) and magnesium granular (336 mg, 14 mmol) were sonicated for one hour in methanol (100 ml). Almost all solvent was removed from the grey reaction mixture on a rotary evaporator to give a viscous grey residue. Diethyl ether (10 ml) and sodium sulfate decahydrate (1 g) were added and the resulting light grey mixture was stirred vigorously for 30 minutes before filtration. The filtrate was dried over anhydrous sodium sulfate and anhydrous oxalic acid (90 mg, 1 mmol) dissolved in Ethanol (˜0.5 mL) was added to the organic phase. A thick white precipitate formed instantly. It was filtered off and dried under vacuum to give 2-oxa-6-azaspiro[3.3]heptane hemioxalate (140 mg, 37%) off-white solid. 1H NMR (300 MHz, CDCl3) δ 4.64 (s, 4H), 4.11 (s, 4H).
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