PAPER 263 Novel and Efficient Synthesis of 2-Aminooxazoles from Pyrimidin-2(1H)-one

Abstract: Stepwise conversion of pyrimidin-2(1H)-one to 2-ami-no-5-aryloxazoles via oxazolo[3,2-a]pyrimidinium salts is report-ed. The sequence involves, (i) regioselective N-alkylation of pyrimidone by phenacyl bromides, (ii) cyclization of obtained 1-(2-aryl-2-oxoethyl)pyrimidin-2(1H)-ones into oxazolo[3,2-a]pyrimi-dinium salts under the action of fuming sulfuric (or triflic) acid, and (iii) reaction of the obtained salts with hydrazine leading to 2-ami-no-5-aryloxazoles. Key words: fused ring systems, ring closure, ring opening, ox-azoles, protecting groups In our previous investigation1 we described a simple route to 5-aryloxazoles IVa bearing a w-aminodienyl residue by ring opening of bicyclic oxazolo[3,2-a]pyridinium salts IIIa (Scheme 1), which in turn can easily be obtained from 2-pyridone Ia via N-phenacyl-2-pyridones IIa. Th