[N+]([C:4]1[CH:5]=[CH:6][C:7]2[O:11][C:10]([C:12]3[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=3)=[N:9][C:8]=2[C:18]=1[CH2:19][C:20]#[N:21])([O-])=O.[OH:22]S(O)(=O)=O.O>O.C(O)(=O)C.[Zn]>[C:12]1([C:10]2[O:11][C:7]3[C:8]([N:9]=2)=[C:18]2[C:4](=[CH:5][CH:6]=3)[NH:21][C:20](=[O:22])[CH2:19]2)[CH:13]=[CH:14][CH:15]=[CH:16][CH:17]=1A solution of (5-nitro-2-phenyl-benzoxazole4-yl)-acetonitrile (1.10 g, 3.98 mmol) (Starting Material 5) was suspended in concentrated H2SO4 /H2O (1/1, 25 mL) and stirred at 100° C. for 30 min. The resulting solution was diluted with water and extracted with ethyl acetate, and the combined organic extracts were dried over anhydrous magnesium sulfate and concentrated in vacuo to give the crude acid. To a solution of the crude acid in acetic acid (10 mL) heated at reflux was added excess zinc dust (1.57 g, 24.2 mmol) portionwise during thirty minutes or until the reaction solution clarified. The mixture was filtered through a Celite® (Fisher Scientific) pad and washed with hot DMF. The solvent was removed in vacuo and residue was suspended and stirred for 30 minutes in 3M hydrochloric acid. The insoluble solid material was collected, washed with water, and air dried to give 2-phenyl-6,8-dihydro-oxazolo[4,5-e]indol-7-one. (Yield 180 mg, 18%).
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