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A mixture of crude 4-oxo-tetrahydro-pyran-3-carboxylic acid methyl ester (1780 g, 11 mol) and NEt3 (830 g, 8.2 mol) in MeOH (3560 mL) was cooled to 0° C. under N2. A solution of 2-chloro-acetamidine (567 g, 4.4 mol) in 890 mL of MeOH was added dropwise over 50 minutes. The reaction mixture was stirred at 0° C. for 30 minutes and then at about 20° C. for 16 hours. LCMS at 215 nm and TLC (DCM:MeOH=10:1) analysis showed that most of 4-oxo-tetrahydro-pyran-3-carboxylic acid methyl ester was consumed. The mixture was then filtered and concentrated to give black oil, which was subsequently purified by flash column chromatography on silica gel and eluted with DCM to give yellow solid/oil mixture, which was further triturated with MTBE (˜1200 mL) and H2O: CH3CN: EA=1:1:2 (˜600 mL) to give the title compound as a white solid (318 g). MS m/z 201.2 (M+H). CHN analysis: calculated (results). C, 47.89; (47.95), H, 4.52; (4.401), N, 13.96; (13.76).

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2. customwas consumed
3. filtrationThe mixture was then filtered
4. concentrationconcentrated
5. customto give black oil, which
6. customwas subsequently purified by flash column chromatography on silica gel
7. washeluted with DCM
8. customto give yellow solid/oil mixture, which
9. customwas further triturated with MTBE (˜1200 mL) and H2O