Di-tert-butyl dicarbonate → 6-amino-5-methyl-4H-3,1-benzoxazin 2,4-dione

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A mixture of the product of step B (13.5 g, 60.8 mmol), di-tert-butyldicarbonate (6.53 g, 30 mmol) and 20% Pd(OH)2 /C (2.5 g) in 200 mL of DMF was stirred under 5 psi of hydrogen for 20 hours. The catalyst was filtered and the filtrate was evaporated under reduced pressure. The resulting yellow solid was triturated with Et2O, filtered, washed with Et2O and dried affording 10.2 g (87%) of 6-amino-5-methyl-4H-3,1-benzoxazin 2,4-dione. This material (9.0 g, 46.8 mmol) was redissolved in 100 mL of DMF and 15.35 g (70 mmol) of di-tert-butyldicarbonate was added followed by a catalytic amount of DMAP was added. The reaction mixture was stirred at room temperature under nitrogen overnight (ca. 30 hours). The reaction mixture was diluted with 200 mL of 1/2 saturated NaCl, filtered, washed with water then with hexane and dried affording 11.1 g (81%) of 1,1-dimethylethyl (1,4-dihydro-5-methyl-2,4-dioxo-2H-3,1-benzoxazin-6-yl)carbamate: Anal. Calc'd. for C14H16N2O5 : C, 57.53; H, 5.52; N, 9.58. Found: C, 57.47; H, 5.80; N, 9.59.

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