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A 22 L three-necked round bottom flask fitted with an internal temperature probe and a mechanical stirrer was charged with the title compound from Example 3 (310.0 g, 1.16 mol) and isopropyl acetate (2.4 L). The vessel was purged with nitrogen and cooled to 0° C. N-methylmorpholine (130.0 g, 1.29 mol) was added dropwise such that the internal reaction temperature never increased above 5° C. The reaction became cloudy. Pivaloyl chloride (150.0 g, 1.24 mol) was added dropwise such that the internal reaction temperature never increased above 5° C. The reaction was stirred at 0° C. for 45 minutes. N-methoxy-methanamine (78.0 g, 1.28 mol) was added dropwise, again keeping the internal reaction temperature below 5° C. The reaction was monitored by HPLC and was worked up when the ratio of the product to starting material was 4:1 (approximately 30 minutes after amine addition). The mixture was then washed with 0.1 M HCl and satd aq NaHCO3. The organic phase was separated and concentrated to a final volume of 1.0 L by distillation. Upon stirring, a precipitate began to form. A 250 mL portion of n-heptane was added, and the mixture was stirred vigorously. The solid was filtered and dried in a vacuum oven at 40° C. to afford the title compound (250 g, 70%).

1. customA 22 L three-necked round bottom flask fitted with an internal temperature probe and a mechanical stirrer
2. customThe vessel was purged with nitrogen
3. customthe internal reaction temperature below 5° C
4. washThe mixture was then washed with 0.1 M HCl
5. customThe organic phase was separated
6. concentrationconcentrated to a final volume of 1.0 L
7. distillationby distillation
8. stirringUpon stirring
9. customto form
10. stirringthe mixture was stirred vigorously
11. filtrationThe solid was filtered
12. customdried in a vacuum oven at 40° C.