O=P12OP3(OP(OP(O3)(O1)=O)(=O)O2)=O.O=[C:16]([C:25]1[CH:30]=[CH:29][CH:28]=[CH:27][CH:26]=1)[CH2:17][NH:18][C:19](=[O:24])[CH2:20][CH2:21][C:22]#[CH:23].[OH-].[Na+]>O=P(Cl)(Cl)Cl>[CH2:20]([C:19]1[O:24][C:16]([C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][CH:26]=2)=[CH:17][N:18]=1)[CH2:21][C:22]#[CH:23]907 mg (6.39 mmol) of P2O5 were added to a solution of pent-4-ynoic acid (2-oxo-2-phenyl-ethyl)-amide (160 mg, 0.74 mmol) in POCl3 (10.4 mL). The reaction mixture was stirred for 2 hours at 105° C. and then poured carefully onto ice. The solution was basified with NaOH 1N followed by NaOH pellets till pH=8. The aqueous phase was extracted thrice with DCM. The organic phase was washed with brine, dried over MgSO4, filtered and evaporated. The crude residue was purified by flash chromatography (DCM/MeOH 99:1) to yield 31 mg (0.16 mmol, 21%) of 2-(but-3-ynyl)-5-phenyloxazole as an orange oil.
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