Synthesis of methoxy-2-quinolones via Pummerer-type cyclization of N-aryl-N-methyl-3-(phenylsulfinyl)propionamides

The thionium ions 10 generated by Pummerer reaction of N-aryl-N-methyl-3-(p henylsulfinyl)propionamides 4 caused not only an electrophilic cyclization reaction producing 2-quinolones 8, but also the formation of the vinyl sulf ides 5 and 6 in favor of the latter reaction. On the other hand, the treatm ent of the vinyl sulfides 5 and 6 with p-toluenesulfonic acid induced cycli zation to afford the 2-quinolones 8 in excellent to moderate yields, depend ing on the electronic properties of the aromatic ring, thus providing a con venient method for the synthesis of methouxy-2-quinolones.