Zn(ClO 4 ) 2 .6H 2 O proved to be a very powerfulcatalyst for the condensation of primary and secondary amines with β-ketoesters to give N-substituted β-enaminoesters.
The reaction between ethyl 2-chloro-3-(phenylamino)but-2-enoate (5) and aniline gave 4-methyl-3(phenylamino)quinolin-2(1H)-one (6) and not, as reported earlier in the literature, the isomeric 2-methyl-3( phenylemino)quinolin-4(1H)-one (1). The latter could be prepared by an alternative procedure. The structures of both isomers were established by extensive NMR spectroscopy including 1D-NOE, 2D-HSQC, and HMBC experiments. Consequently, the reinvestigation of the title reaction revealed an unexpected simple access to never 4-alkyl-substituted 3-(arylamino)quinolin-2(1H)-ones.