[CH3:1][CH:2]1[CH:6]([C:7]([O:9]C)=O)[C:5](=O)[CH2:4][O:3]1.[CH:12]([NH2:14])=[NH:13].C1(C)C=CC=CC=1.C([O-])([O-])=O.[Na+].[Na+]>O>[CH3:1][CH:2]1[C:6]2[C:7]([OH:9])=[N:14][CH:12]=[N:13][C:5]=2[CH2:4][O:3]1A mixture of methyl 2-methyl-4-oxotetrahydrofuran-3-carboxylate (8.3 g, 52.8 mmol), formamidine (7.0 g, 68.6 mmol) and toluene (200 mL) was heated to reflux under Dean-Stark conditions overnight. The mixture was allowed to cool to room temperature, diluted with water and neutralized by the addition of saturated Na2CO3. The organic layer was separated and the aqueous layer extracted with EtOAc (5×200 mL). The combined organic layers were dried with brine, MgSO4 and concentrated. The residue was purified by column chromatography (100% EtOAc to 5% MeOH:EtOAc) to give 5-methyl-5,7-dihydrofuro[3,4-d]pyrimidin-4-ol as a brown solid. 1H NMR (DMSO-d6, 400 MHz) δ 12.58 (s, 1H), 8.18 (s, 1H), 5.18 (bs, 1H), 4.82 (d, J=14.4 Hz, 1H), 4.72 (d, J=14.4 Hz, 1H), 1.37 (d, J=6.8 Hz, 3H).
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