[Cl:1][C:2]1[N:11]=[CH:10][C:9]2[NH:8][CH2:7][C@@H:6]3[CH2:12][O:13][CH2:14][CH2:15][N:5]3[C:4]=2[N:3]=1.[C:16]([O:19][C:20]([CH3:26])([CH2:22][CH2:23][CH:24]=O)[CH3:21])(=[O:18])[CH3:17].C(Cl)Cl.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+]>[Ti](Cl)(Cl)(Cl)Cl>[C:16]([O:19][C:20]([CH3:26])([CH2:22][CH2:23][CH2:24][N:8]1[CH2:7][C@@H:6]2[CH2:12][O:13][CH2:14][CH2:15][N:5]2[C:4]2[N:3]=[C:2]([Cl:1])[N:11]=[CH:10][C:9]1=2)[CH3:21])(=[O:18])[CH3:17](R)-2-Chloro-5,6,6a,7,9,10-hexahydro-[1,4]oxazino[3,4-h]pteridine (PREPARATION x3, 200 mg, 0.882 mmol) and 2-methyl-5-oxopentan-2-yl acetate (55.8 mg, 0.353 mmol) were combined in a 25 mL pear flask to give an orange suspension. Titanium(IV) chloride in DCM (1M, 0.971 mL, 0.971 mmol) was added at room temperature to give a deep-red suspension, which was stirred at room temperature for 1 hour before being cooled to 0° C. Sodium triacetoxyborohydride (281 mg, 1.324 mmol) was added at 0° C. in portions. The thick suspension slowly turned into a thinner, orange one with gas evolution. UPLC showed the reaction proceeded more than half-way after about 20 minutes. The reaction mixture was carefully quenched with brine, and was partitioned between saturated NaHCO3 and ethyl acetate. The aqueous layer was extracted a second time with ethyl acetate. The combined organic layers were dried over MgSO4, filtered, and concentrated to give the title compound, which was used without further purification. ESI-MS m/z [M+H]+ calc'd for C17H25ClN4O3, 369.17. found 396.2.
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