Formic Acid → Ethyl oxazole-4-carboxylate
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C(O)=O.C1N=CN([C:9]([N:11]2C=N[CH:13]=[CH:12]2)=[O:10])C=1.[N+](C[C:19]([O:21][CH2:22][CH3:23])=[O:20])#[C-].CCN(CC)CC>C1COCC1.O>[CH2:22]([O:21][C:19]([C:12]1[N:11]=[CH:9][O:10][CH:13]=1)=[O:20])[CH3:23]C(O)=O.C1N=CN([C:9]([N:11]2C=N[CH:13]=[CH:12]2)=[O:10])C=1.[N+](C[C:19]([O:21][CH2:22][CH3:23])=[O:20])#[C-].CCN(CC)CC>C1COCC1.O>[CH2:22]([O:21][C:19]([C:12]1[N:11]=[CH:9][O:10][CH:13]=1)=[O:20])[CH3:23]To a sol. of formic acid (8.62 mL, 228 mmol) in dry THF (200 mL) was added portionwise CDI (37.05 g, 228 mmol), whereas a gas evolution occurred. The mixture was stirred for 30 min, and a sol. of ethyl isocyanoacetate (25 mL, 228 mmol) in Et3N (60.5 mL, 434 mmol) was added to the reaction mixture. The mixture was stirred at rt for 1 h, then under reflux overnight. The reaction mixture was allowed to cool to rt. Water was added, and the mixture was extracted with Et2O (3×). The combined org. extracts were dried over MgSO4, filtered and concentrated. Purification of the residue by FC (EtOAc/heptane; 1:5 →1:3→1:1) yielded the title compound (27.2 g, 84%). LC-MS: tR=0.58, ES+: 142.07.
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